So, again you need to submit your visa application to Chinese embassy there in Pakistan. The requirements are as follows:
1. Original Visa Notice Sheet from an authorized governmental apparatus /organization in China
2. Alien Employment License of the P. R. China /Working Permit by the State Administration of Foreign Experts Affairs, P.R. China /Letter of Invitation for Foreigners Engaged in Offshore Petroleum Operations in the P.R. China/Registration Certificate of Foreign Enterprises Permanent Office inChina
3. Physical Examination Record for Foreigner and attested by Ministry of Foreign Affairs of Pakistan
4. Employment Contract
5. Your Employer's Company Registration Certificate in China (copy)
Meanwhile, your previous China visas are helpful for your application this time.