Mr.Li, it is hard to say whether you can apply for China visa in Islambad or not, sometimes, the China embassy refuses to issue China visa to non resident applicants. The work permit or residence permit of Pakistan is required.

You don't need to provide the following supporting documents if your former nationality is Chinese. The regualtions are: First time applicants whose former nationality was Chinese, shall write down his Chinese name in the application form and submit his original Chinese passport or the photocopy of the information page of the passport. Applicant who was formerly Chinese and has acquired a new foreign passport, if there is a Chinese visa in the old passport, shall submit his old foregn passport or the photocopy of the Chinese visa.