Those airlines belong to the civil aviation, what is the difference between civil aviation and the national airline

All airlines are civil aviation whether they are passenger, cargo, or sowing and spreading medicine. Air China is just the name of one of the airlines in civil aviation. You should be asking which ones are national airlines and which ones are private.

Air China, China Southern Airlines, China Eastern Airlines, and city-named airlines like Hainan Airlines, Beijing Airlines, Capital Airlines, Sichuan Airlines, Xiamen Airlines, and China Postal Airlines are all basically state-owned, or have some state assets.

Such airlines as Spring Airlines, Lucky Air and SF Airlines are privately owned. But they all belong to civil aviation.