Abstract: In order to solve the defects in resistance spot welding of the stainless steel rail vehicles，such as the poor appearance，poor sealing and low efficiency，the application of partial penetration lap laser welding technology in rail transit stainless steel vehicle car-body welding is studied，including the principle of partial penetration laser stack welding， parameter optimization test， micro-structure analysis，fatigue performance analysis and the structural improvement of laser welding stainless steel vehicle sidewall are systematically studied. The research results show that the surface condition and fatigue strength of the car-body are improved，the car-body structural strength is higher than the requirements of En12663 standard.