Nudism outside isn’t exactly against Chinese law, but it is frowned upon under Confucianism, as it goes against Kongzi’s ideals of propriety and shame. On the other hand, there are plenty of people who believe that there’s no shame in baring the human body in all its undressed splendour (NSFW). There is actually places to be social naked outside,
The only reported naturist beach in China (as I know of) is Sanya, Hainan Island, Dadonghai Beach in the north end/free beach. This is a quite public and touristy place, with at least 500 Chinese visitors a day, and a few Europeans. Children is playing everywhere and having fun on the beach.
There are other indoor possibilities as a naturist, but China is not a very Naturist friendly country, even though it is legal.
Update!!! In 2014 Sanya naturist beach was closed by the government. According to China News Service – “Violators will be punished in accordance with the nature of their offence”. More info in this article on Daily Mail.