I don't know how can I apply for Employment Visa.

Malik, according to what I know, Pakitstanis are unable to apply for individual tourist types. So you have to apply for a Z type directly. It requires the work permit issued by local labor bureau. First, you need to find an employer and apply for the work pemit with his help. It requires that you should have bachelor's degree and related working experience. After getting the work pemit, then you need go to appointed hospitals to do the physical check. If everything is fine, then you should bring your passport, application form, a recent passport photo, work permit and physical check result to Chinese embassy. It takes four working days to deal with your application.

If you are lucky, you will get your Z on the fourth working day. Then you need go to PRC as soon as possible because the Z type's duration is just 30 days. When you arrive, you need change your work permit into the alien's employment certificate and then go to local entry and exit management bureau to change your Z into a temporary resident permit. All these things have to be done within 30 days.

It doesn't matter whether you entered PRC before. The most important thing is that you find a qualified employer who is willing to recruit you and prepare all required documents.