In my experience you needn't undergo another medical exam after arriving in China if the medical from your homeland is satisfactory, provided that the date of that medical is within 90 days of the date of issuance of your residence permit.
Also be aware that if you have a medical in China, it'll have to be done at the designated hospital in the provincial capital for foreigners and for Chinese who will go abroad, as that hospital will have advanced medical equipment as well as a lab for diagnosing HIV+. The Aids Test result will be available two or three days later.