Hi I am Pakistani I have girlfriend chinese and we decide to marry so what i have to do

1. you need to get unmarried certificate and consent letter from the Chinese side (your girlfriend),
2. you get the single status certificate from Pakistan
3. then make single status certificate from Pakistan attested by the Foreign Ministry of Pakistan, Islamabad
4. go to China embassy in Pakistan to apply for authentication

You should submit:
1. single status certificate and the photocopies;
2. Completely filled AUTHENTICATION/ATTESTATION APPLICATION FORM; stating clearly which documents (names of the documents) you want attestation and the reason/purpose for this attestation.
3. Photocopy of valid passport and ID card of the applicant.
4. If single status certificate are in Urdu, an English/Chinese translation is required.
5. unmarried certificate and consent letter from the Chinese side (your girlfriend)

I again from where we get this unmarried certificate and consent letter who give us these letters. 2nd thing i am not going china for marriage i am going pakistan for marriage i just want to know that after marriage is there any deficulty for us to visite china or not

If you get married in Pakistan, you don't need to get the single status certificate from Pakistan, but your fiancee needs it.

After the marriage, it won't be difficult for you to visit China.