I was vegetarian before I went to China and I have been vegetarian since I returned from China, but I was not vegetarian while in China. In theory, it isn't impossible to be vegetarian. There is a rich vegetarian tradition in China and many Buddhists (mostly older people) still chose to be vegetarian. I did meet a few people who were working in China and managed to remain vegetarian throughout their stay. However, they lived in cities and had a number of eating options.
I lived in a private boarding school and I ate at the school cafeteria, so being vegetarian wasn't really an option for me. In theory, I could have cooked for myself at home, but given how drastically I would have had to change my eating habits, I probably wouldn't have done a very healthy job of it. Instead, I was able to sample all sorts of interesting foods (chicken feet, for instance) and eat a lot of vegetables out of the dishes with meat in them.
More importantly in my decision to eat meat was the fact that it was very difficult to explain vegetarianism as a lifestyle choice. The vegetarian tradition in Chinese history was primarily based on need and economics. Now that most Chinese are doing better economically, they can afford meat occasionally. However, it is still a sign of status to have meat on your table and is an absolute necessity if you have a guest over, especially a foreign guest. For me to turn down meat dishes would have been like saying, "I don't think you are rich enough to afford this, so I won't eat it."
Even in the face of all these obstacles, I could have remained vegetarian if I had really tried. I'm willing to admit that I didn't stick as closely to my principles as I would have at home. But it was a matter of how to expend my energy and how much I was willing to lie. If I had been willing to say that I was vegetarian because of religion, it would have been simple. But I am willing to eat meat for cultural reasons before I lie about religion.
If being vegetarian is something that you are not willing to give up and you want to visit or work in China, it is possible to remain vegetarian if you work at it. However, it will be work to ensure that you don't get meat dishes. By the time a close vegetarian friend came to visit me at the end of the year, I was able to keep him fed without having to compromise his vegetarianism. I had finally figure out a way to explain his choice in a way that made sense to our Chinese hosts and was actually constructive in building friendships. I explained that he believed very strongly in peace. So strongly, that we should even be peaceful to animals. Because visitors are often seen as Western Ambassadors, this sort of explanation usually goes over really well. For my friend, it got him a number of drunken hugs from businessmen at a banquet.