Your employer, the French company in China should give you the below two documents before you return to Iran:
(1) The Employment Permit for Foreigners issued by the Ministry of Human Resources and Social Security;
(2) Visa notification issued by an authorized unit in China (original)

You also need to prepare the following documents:
(i) Original passport which has more than 6 months left before it expires from the date of application and sufficient blank visa pages (18 months and more left if intended stay in China is more than one year).

(ii) One completed Visa Application Form (e-Form / Download) with a recently-taken passport photo. All the items on the application form should be fully filled in with genuine information;

(iii)"Physical Examination Record for Foreigner" issued by doctors from an Indian state hospital. The photo on the Record should be stamped by the hospital.(Valid for 6 months from issued date)