Abstract: Variable polarity plasma arc welding process is an important method for welding aluminum alloy.Experimental results show that in addition to current and welding speed, gas flow rate, shrinkage of tungsten and the height of the nozzle are very important parameters which influence weld characteristics.The surface Gauss heat source and the cylinder heat source were selected to simulate the welding temperature field.Through a lot of experiments, the effect of main process parameters on variable polarity plasma arc welding was analyzed.By finite element analysis method, the relation between the heat source model and practical process parameters was established, and through linear regression analysis method mathematical formula was set up.