Abstract: A three-dimensional unsteady model of double pulse tangsten inert gas (TIG) welding pool is developed. By choosing appropriate boundary conditions, thermal properties and strongly coupling the control equations, the cyclically change regulations of temperature field, flow field and depth and width of the pool are obtained. The cyclically change regulations of pool size are obtained. The results show that the pool size with double pulse current is larger than that with average currents. The variation of pool size lag behind the pulse current is larger, especially under the action of the high energy pulse current and under the action of the double pulse current. The flow velocity is also larger and the stirring effect is stronger within the pool.