Abstract: A study on fluid flow in the molten pool of laser deep penetration welding process was carried out which utilized the finite volume method.A three dimensional fluid flow model was established and the effect of the laser beam was represented by the Gaussian rotating body heat source.The temperature field,fluid flow and weld shape were calculated considering the Marangoni effect.The temperature field contours,the welding thermal cycle curve of molten pool and the velocity field of molten pool were analyzed based on the calculated results.Finally, the laser welding experiment was carried out with the same weld parameters.The actual weld shape was observed.The simulation results and experiment results were comprehensively analyzed.The accuracy of the numerical simulation results was verified.The calculated geometries of the molten pool and welds were more similar to that of the experimental results when the Marangoni convection was considered.