You need to apply for work visa (Z visa), the requirements are:
1. A notice of visa authorization from a duly authorized Chinese organization
2. Alien Employment Permit
the above 2 documnets should be provided by your friend
3. Covering letter from applicant addressed to the visa office.
4. Physical Examination Record for Foreigner
5. your passport and its copy
5. one filled visa application form affixed with one passport photo