Abstract: The pressure,shape and thermal density of a welding arc will change under high-pressure and strong-cooling underwater environment,so will the heat exchange on the workpiece surface. In this paper,a FEM model of the thermal process of underwater wet gas metal arc welding was established using SYSWELD. Two remarkable characteristics of underwater wet welding-the water compressing action on the arc and the enhanced heat loss caused by the surrounding water-were considered in the model by adjusting the heat sources and convection coefficient on the workpiece surface. Then thermal cycles and weld pool profiles under different water depths and different water flowing speeds were obtained. The calculated results show that the weld pool became deeper and narrower in deeper water,and so did the profiles of the isotherms. And the results also revealed that the weld pool and profiles of isotherms became narrower and shallower when the water flowing speed increased.