Abstract: According to the theory of hydrodynamics and he at transfer mechanism,a transient three-dimensional finite element mode has been developed to simulate numerically the fluid flow & heat transfer of the puddle in keyhole-mode plasma arc welding in this paper.Based on the data of the heat transfer,the shape of the pool & forming process of the keyholing puddle were shown by computer graphics.Relevant computation proves that the finite element mode can be used to calculate the fluid flow & heat transfer,and simulate the shape of the pool & forming process of the keyholing puddle in keyhole-mode plasma arc welding.It is demonstrated that the model provides a theoretical guide for practical application of keyhole-mode plasma arc welding.