Abstract: The shape of welding pool in laser deep penetration welding was calculated based on continuity equation, momentum conservation equation and energy conservation equation using FLUENT solver. Solidification/Melting model and κ -ε model were used. Simulation results showed that the recoil pressure on the front wall of the keyhole is an important driving force of welding pool fluid flow because of large temperature gradient in the front part. The larger size of the solidification transition zone of welding pool in the liquid-solid interface was related to solidification heat.