You have to bring your passport and an official certification of your marriage status, i.e. never married, divorced or widowed. The certification needs to be legalised by the Chinese embassy in your country. So before travelling to China, you need to consult with the Chinese embassy first.

After entering China, you need to go to local marriage registration office to submit your marriage application with your fiancee in person. In most cases, you also need to have a health check at a designated hospital. The marriage certification will be issued once the application is ratified.

However, the following Chinese citizens are not allowed to marry foreigners:
militants, police officers, governors and prisoners