There's a few churches in the PRC, but Beijing serves (fortnightly?) in an embassy church (Fr Sergei) and Shanghai has probably returned to a room in the embassy (with weekly services), after being in a former Orthodox church for the duration of Expo.
Beijing and Shanghai require you to be a foreigner to enter (showing a passport to guards and all), and in Beijing's case, you have to have your name placed on the list beforehand (an e-mail should suffice).
There are other parishes dotted around China - I believe Guangzhou has one, and Xinjiang as well...and, of course, two in Hong Kong and one in Taiwan (depending on your political views). The best resource is probably orthodox.cn - Mitrophan is doing a great service for those interested in Chinese Orthodoxy.
Hope this helps!
Great site, thank you very much!