Abstract: Numerical analysis of heat transfer in gas tungsten arc welding (GTAW) process was conducted with ANSYS software. The calculated results of transient evolution of isotherms during continuous welding for 20 s and cooling for 20 s show that the workpiece was completely penetrated at 5 s after the arc was struck,however,the molten pool totally disappeared within 1 s after the arc moved away. During the welding process, the high-temperature region moved simultaneously with the arc. When the arc moved away,the cooling stage began,the zone with high temperature gradually moved backward (relative to the welding direction) and cooled to ambient temperature. The predicted thermal cycles at different points with the same intervals on top surface along the welding direction displayed that the temperature rising curves have the same trend in quasi-steady state, while clear differences existed between the temperature decreasing curves because the latent heat was released when the molten metal solidified. The temperature decreased faster at points closer to the weld crater. The influences of welding current,welding speed and concentration parameter on the heat transfer were analyzed, and then these parameters were optimized.