Abstract: The formulation of hole due to the flow of molten metal during welding was numerically simulated. A two-dimensional axial symmetric model was established by determining the control equations and boundary conditions after analyzing the physical process of welding. Melting and solidification model and heat source model were built based on commercial software Fluent. The interface between the metal and gas phases was tracked using VOF model, which induced formation of holes in fluid flow on sheets with different thicknesses. The reasons of shaping holes was analyzed with the fluid flow field and temperature field. The microstructure of bead weld was observed with tin-lead alloy as experimental material, and it shows that the simulated results agreed well with the measured results.