You can apply for China Tourist Visa, you can prepare the required documents in person, if you apply for other types of China visa, you need the invitation letter and other certificates from China side.

Required documents for Tourist Visa:
(1) An original copy of passport with enough blank visa pages, valid for at least another 6 months.

(2) A fully completed copy of Visa Application Form signed by the actual applicant; all applications prepared by people other than the applicants (except those below 18 years of age) should be properly signed by the applicants themselves; for every application prepared by a travel agency, both the agency's seal and proper signature of the actual applicant should be visible.

(3) One recent 22(in.)-sized color passport photo, white in background, with a full front view of the applicant's head and shoulders but without any head cover.

(4)round-trip flight ticket, your Thai visa and its copy

(5)other documents required by visa officer.