what documents would be required for a 12 month multiple entry visa to China?

12 months multiple visa to China is very difficult to get nowadays, but you can try to fll this to your application from. For business purpose, you need invitation letter from both your inviter company and by an authorized unit in China, like foreign affairs. And letters of invitation can not be email, and should include full name and passport number of the invitee as well as the purpose and duration of the visit. The processing time needed from Chinese embassy is 4 working days. If your family want to join you, their name should better be mentioned in the invitation letter, providing certificate of your relationship as well.