If he is going to stay in China for less than 6 months, he needs to apply for a Business (F) visa. The documents are as follows:
1. A valid passport as well as a copy of its information page (6 months validity and one blank visa page).
2. Application form for China
3. one recently-taken color photo.
4. Visa Notifications Form from an authorized Chinese Unit, or invitation letters from the host company, meeting or exhibition organizers in China, or an introduction letter from applicant's US company, etc.
5. the original and a photocopy of certificates for permit for residence, work, study or valid US visa.
Besides the documentations mentioned above, other documents might be required by visa officers.