Abstract: Presuming a 3-D static conical heat source,the process of plasma arc welding is simulated with a computer.Using ANSYS,the three dimensional flow of the welding pool,the temperature fields and their transient variation processes are calculated,and the flow style and velocity of molten metal are investigated.Simulation with Gauss heat source is also done for comparison.Corresponding welding experiments such as terminal voltage signal and the dimension of weld size are measured to prove the reliability of the model.