Abstract: In order to meet the technical requirements for the penetration and width of SUS301L stainless steel laser lap welding for subway roof, the influence of welding parameters on the penetration and width was analyzed using numerical simulation technology. The design of parameters were optimized through orthogonal test which obtained the process parameters of laser welding SUS301L stainless steel sheet. The results show that the optimal parameters of laser welding of SUS301L stainless steel sheet is that the laser welding power of 1050W, welding speed of 36mm/s, defocusing amount of 1mm, the flow rate of shielding gas of 25L/min. With the optimal parameters, the width and penetration are respectively 1216.4μm and 407.4μm. The good consistency between the simulation results and the experiment results shows that the correctness of the simulation model can be established in this paper, which can provide reference for the construction of the later process database. Under the optimal welding parameters, the surface of the weld is silvery, continuous and complete, the weld area is isomer and column crystals, and the average shear strength of the weld is 2559.96kN.