Abstract: It is of great theoretical significance and engineering value to numerically simulate welding process. Numerical simulation of plasma arc welding is one of the key ways to study the mechanism in PAW and to optimize the PAW parameters. The treatment method of keyhole is taken as the classification basis. The PAW models contains four kinds,which are PAW model without considering the keyhole,PAW model with assuming keyhole shape,PAW model with tacking the keyhole,and PAW model with both tacking the keyhole and coupling the keyhole.The advances in PAW are demonstrated and reviewed in this paper.