I will go visit my father in China, how long I can stay for one entry visa?

If your father is a Chinese residencing in China, you can try to apply Q1 and you can stay for around half a year to three years. The exact duration is decided by the local PSB where you father live.
If he is a foreinger living or working in China, you can try to apply S1, which has the similar duration with Q1.

If you just want to visit him and do not want to stay very long, you can just apply for a L type which you can stay for around 30 days.