The current stainless steel railway vehicles body and structure are usually assembled by resistance spot welding process. The weak points of this process are the poor surface quality and bad airtight due to the pressure of electrodes. In this study, the partial penetration lap laser welding process was investigated to resolve the problems. The effects of the laser welding process parameters such as laser power, welding speed and focused distance to the shape of the weld seam and the shear tensile strength were discussed to find the optimal parameters. And the mechanical tests and microstructure analysis were also taken in this study. The optimal parameters are P=2.0kW，S=22mm/s，F=0mm. This work has great significance of improving the manufacturing level of stainless steel railway vehicles.