Abstract: The qualitative analysis is carried out on the behavior of the partial penetrated weld pool with welding current changing from pulsed peak value to base value during pulsed TIG welding.The mathematical model of the liquid surface shape of partial penetrated weld pool is developed.The numerical simulation process based on this model is finished by Surface Evolver,a FEM simulation software.Both the simulation results and the model are then modified with experimental results.The modified model lays the foundation for systematical and qualitative simulating the principles of liquid surface of partial penetrated weld pool under various kinds of condition,and for obtaining the relationship between feature value of upper liquid surface and depth of weld pool.