I worked within China's Olympic program and team, as a Westerner/Foreigner, thus have had rare chance to view it from within. I can thus provide a better answer, one from what I know and viewed, from foreigner and western perspective.
Before my answer, firstly I like correct some false bit of information presented already. Lot of false information presented in the western media, or 'glorified' articles made for mass reading. Some information in media is true, but a lot is false. Most have ignored the culture, the context, and the sports society of China. The fact that the majority of those 'torture' images, and information that have been used in Western media came from a reporter that went to 'random' training centers or private classes. This is not the Olympic training; thus voiding any conclusion from that source. Furthermore to make generalisations based on 'journalist selected' emotional photos taken at one school, and generalise them to an entire country is a rather false conclusion. In the same way that taking 10 photos of angry football coaches in UK (cue a few premier league coaches here), and then generalise that to say 'UK Football is Abusive' would be false conclusion to make also.
However not to say that athletes within China's Olympic program don't train hard, they do, it's elite sport after all (elite sport around the world trains hard). And there is research that does suggest that they do experience high rates of injuries from their traiining. But in context of the so-called torture (as in those photos), well i have never seen it, seen lots of smiles though!!.
In terms of athletes from a young age, training hard, and often away from families to go to training centers, this is true, but one needs to understand the context within China, the opportunities that present to these athletes (pay, education, better life), and these athletes’ background (from low socioeconomic families), before passing simple judgment. I will elaborate on this below at the bottom, as I also did in comment on someone else's answer.
These facts below however are true of why China athletes succeed at the Olympics:
1) The Chinese train harder than anyone else in the world; as other foreign coaches working with China's Olympic Team have stated in media in past: The Guardian. Following Confucius beliefs, the Chinese believe hard work gets results, and following a progressive long-term athletic development model with repetition of technique and skill they perfect every movement until optimised (thus why they succeed in sports like table tennis, diving, gymnastics, and even weightlifting requires perfection of technique).
2) Centralised Training Program with High Government Support & Funding: The Chinese government has a heavily fund and centralized top-down training model; with the one goal to achieve Olympic Gold. The exact figures of the funding are unknown, and not as transparent as other nations, but still estimated to be the highest funded high performance program in the world. These funds help to pay athletes’ salaries, have full-time staff supporting those athletes, get the best coaches & foreign expertise to improve it further, build big training facilities, and really do anything they want. With a structured pyramid program, with around 5000 sports schools, filtering into province training centers, and then the best up into the Olympic center. Ensuring that the Chinese Olympic program can run smoothly and succeed at its goal.
3) Foreign Expertise: The big jump made at Beijing 2008 and beyond, had a lot to do with foreign expertise. The sourced the world for the best coaches, the best staff. Head coaches alone, there were 28 foreign coaches for the last Olympics; so to say Chinese coaches are "torturing" kids, then ask yourself but what about the foreign coaches? I even know examples where athletes get injured and they fly in experts from around the world for their opinions. This spending of money for an athlete is rarely done elsewhere.
4) Strong talent Identification and Long-term Athletic Development Model: At young ages they look for kids who have the physical capabilities that will allow them to succeed in a sport, and then build on-top of that strong base with a long-term athletic development plan. E.g., start with basic skills and foundation until that is perfected, then build on top of that with another skill, etc.
5) Top-down sports system vs. bottom-up: China is a top-down sports system, a system where the top level controls and manages everything with the goal to achieve Olympic success. Meaning the entire reason athletes enter the system at the bottom (the sports schools), is with the aim to achieve the government’s goal of Olympic success. Some other Asian nations however have similar systems. This contrasts however to Western nations, whereas it's a bottom-up system, whereas the community and club levels develop athletes, and athletes enter sport for their own goals. One where they just naturally develop going through lower levels, until they have a talent, and then get recognised and selected for national program (and not until then does the government or national sports governing body have much influence on that athlete’s life). Of course arguments and debate on which is optimal. However it's not hard to see that if you have a control of athlete’s life and sports development from the day they enter sport, and plan & goal for those athletes to succeed at Olympics, then it is much easier to plan for accomplishing that goal (in point 4 above), e.g., what education do they need, what skills do they need, what physical requirements do they need, how much sleep do they need, what medical support do they need, etc.
6) Year round structured training (More prepared): Not to say not all athletes train year round, but the Chinese have a 365 days/year training together as a team generally in most sports. Although some sports like Basketball they have around 6 months (as they spend the other 6 months in their professional teams), but that's still lot more time together in national team than other nations. What does this mean? Well it means they are going to function better as a team, be more prepared to work with the national coach, better skilled, and better in team environment & teams culture, and with the physical resilience and technical skills to succeed. A lot of other programs in Olympic sports around the world do not follow such a professional program, for example some Olympic teams athletes train independently and then only come together to join the national team in the months or even just weeks before the games.
7) Smart Allocation of Funding: They concentrate on sports that they can win, or succeed at, be it sports that they see an opportunity (less competitive) or sports that they know they win (e.g., table tennis). For example many gymnasts are changed into snow boarding, aerial skiing, and diving. Because of the Chinese athletes’ great gymnastic abilities, they thus would make a good for a similar sports that requires these skills to help and thus can become more competitive then people without those same gymnastic abilities. They also focus on sheer medal numbers; they concentrate on sports with different weight classes (e.g., weight lifting or wrestling) or sports with more medals (e.g., swimming). But then this same approach is done by most centralized sports systems, including Australia.
8) Repetition of Skill or Technical Focused Training: the old rule, repeat until you are perfect or 'practice makes perfect'. Very much following Confucius thinking here, in China the kids do ONE sport, and repeat the same skill over and over, day in and day out. This is something not done or rare in many nations, for example kids in Australia or America would play many sports in their childhood, they develop better motor skills and coordination but not fine tuning one skill like the Chinese. Is thus the reason China often succeed in technical focused sports like table tennis, diving, gymnastics, because they have trained until they perfected the routine. However all sports do have a technical focus, even track & field, weightlifting, and swimming; related to efficiency and ease of movement.
9) Rewards for Athletes & Better Life: The rewards for those who make it are great. Some Olympic athletes earn more a week than their poor family can in a year. That way it’s a great way forward for poor families to jump to a better social class. This provides excellent motivation for them to train hard. China Olympic champions are suggested to get $200,000USD for an Olympic Gold (figure appears to vary in different sources), and add in houses, a high level job within the government upon retirement; even winning the All-China Games grants athletes $100,000USD (depending on the province). Most of these athletes come from families that work in factories, and/or farms, earning just enough to feed the family.
10) National Pride: sports is seen as a sign of power similar to GDP. A collective culture still, looking to better the community they are within. They do it for the family, nation, and less for themselves (opposite to the west). A way to show a strong and powerful nation.
However above all, one big factor: they want it more than anyone else in the world (similar to the Kenyans in distance running), that motivational factor is big thing in elite sport.
#Also important thing is the numbers? ......
Yes China does have one of the largest talent pools in the world to pick from. China has around 200,000 full-time athletes within their Olympic or Institute of Sports programs. Probabilities of "1" champion being produced out of that talent pool is thus much more likely, in comparison to the 1000 or few 1000 in other Olympic programs. Also the width and differences of the 'ethnicities' across China mean they get various people of different physical capabilities. But at the same time, you could consider the fact that USA has 36 millions kids playing organised sport, whereas China has few kids outside of the sports programs playing sports (until recent years). Yes China has more athletes in their Olympic program, but in total, their athlete talent pool was* actually less (*China's rising middle class, & recent sports reforms have changed this, and now sports in public and community run level are becoming more common). However talent pool just means they have more to pick from, but they can still only send same number of athletes to the Olympics as other nations, and they still need to develop that talent into something. Similar example would be India, they have a large population yet they don't go well at the Olympics. And despite the country being crazy for cricket, they still get beaten in cricket by many small populated nations like Sri Lanka, Australia and South Africa.
Ps: People write on the Torture (as one other answer did). But you need to put this into Context:
These articles are not true representation by the way, similar to a lot of western media's take on China. A total different context one firstly needs to understand. I work for the Chinese Olympic Team as a foreigner; so my opinions are West but I see the truth in the East.
In the West kids enter sport for enjoyment, or a hobby, their families can easily feed them and provide good education, their is no reward from the sports for that kid. Yet still in the West like America or Australia, parents torture kids also, e.g., parents glory with pushing little kids into ballet or football, you see parents screaming at their kids on the sidelines almost every weekend at the local u12 football game.
But in China it's different context altogether. Athletes usually come from poor rural provinces, where their families cannot afford to send them to school, and where the kid needs to work in a factory for 14hrs/day, or on the farm doing hard labour just to feed the family. Now they enter sport, the family is happy, because now these athletes get food, accommodation, education, etc.... That ignoring the fact to start with that these photos are not even taken at an official sports school in China. And that athletes anywhere in the world train hard.
Within the Chinese Olympic program, when the athletes get selected many feel that they are actually lucky. Some become very wealthy, with many of my athletes driving fancy cars that not even I would afford (Bentleys, Porsche, you name it). Gain houses, high positions in government, and around 200,000 USD for an Olympic Gold medal. However that said, of course not all make it, only the select few do. Most do not. But still the ones that do not are given accommodation, food, education, and now they get university degrees. Now not only whilst as an athlete do they have opportunity for pay that is better than the factory or farm, now have opportunity for good degree and future employment that would have never been possible based on their socioeconomic background. And now they work less hours then they would have been doing following their normal family path working within the factory or the farm. This is easier (or less torture) then what they would have been doing before.
Thus they now have:
-Better Pay
-Accommodation & food provided
-Less hours/easier than a 14hr+ shift in a factory in China.
-Education (university)
-Medical Treatments.
We need to put in context of the nation, & the culture!!
source: https://www.quora.com/Why-is-China-so-successful-at-the-Olympics