Ms.sara, your friend can apply for L visa for visiting friends, you need to send her an Invitation Letter, the copy of your passport, the copy of your X visa and Residence Permit, your college can give you a certificate that you study in the college, if she has the above documents, she just need to prepare the following documents by herself:
I) Original passport with validity more than six months and minimum 2 blank visa pages;

(II) Photocopy of the first 2 pages (personal information) of the passport and the recent Chinese visa page if there is any;

(II) One fully completed visa application form in Chinese or English, attached with one of the applicant's recent color photograph (30mm X 40mm)

TO,
Mr,Albert
thanx alot for your answer.he (my friend) lives in saudi arabia and he is also pakistani some body told me that he wants offical invitation letter from any Govermenst Beru in china.and he will be travel on F type of visa. cud you plz conform this ?

for visiting friends, the official invitation letter from any govenment office is not required, your friend doesn't need to apply for F visa. He can apply for L visa.