You can apply for a Multi-entry L tourist visa for 12 months from the Chinese embassy in Pakistan with the documents below:
a. Your passport with blank pages and at least 6 months validity left before expiration.
b. A truly and completely filled Multi-entry visa application form affixed with one passport-sized photo.
c. Proof of requent visit to China.
d. Invitation letter from your friend in China enclosed with his/her valid address and contacts in China.