Abstract: The numerical model,including some effect factors such as surface tension,flotage,interaction force between liquid and solid,turbulent,welding velocity,convection and radiation,was founded for laser deep penetration welding processes,and the evolvements of the temperature,the flowing and the weld profile in the molten pool were forecasted.The results show that the trend of broaden in the molten pool is larger than that of elongate,the main heat transfer method in the upper of molten pool is the convection,but that in the lower of molten pool is diffusion,and the main force for the broadening and elongating in the upper pool is Marangoni force.The results of the high speed CCD camera and Katayama's X-ray image are well agreed with simulation results.