want to visit CMEF 2015, in may 2015. what Visa required and the documents are required?

You should apply for a M type. It requires the following documents apart from your passport, application form and photo.
1. invitaion letter from CMEF.
2. invitation letter from duly authorized Chinese unit (referring to local foreign affairs office)
3. an introduction letter, in which it states where you are going to, who invites you, the inviter's name, address and tel.
4. other documents required by the consulate (if any)