There are not a marriage visa of China, he can stay in China for about 30 days, he can asks for a longer stay duration on the visa application form, the final decision is up to the visa officer. He need to prepare an Affidivate of Single Status from a local notary office, then authenticated by Foreign Affairs Ministry of Pakistan and Chinese embassy/consualte in Pakistan. You can send him the copy of your Chinese passport or ID card. When he apply for China tourist visa which is issued to aliens coming to China for sightseeing, family visit or other personal affairs, he can specify his purpose of coming to China for make marriage registration with a Chinese girlfriend.