Research on laser scanner welding technology of three-layer lapped steel structure of car body was carried out in this paper by 6 kW laser. The influences of defocusing distance, welding speed, welding power on weld width, weld depth, bonding layer width and typical defects were clarified. The process window was established and well-formed welding joints were obtained. On this basis, the tensile strength of the joints were further analyzed and compared with those of the resistance spot welding joint. Results indicate that the maximum tensile strength of the laser scanner welding joints is 12.64 kN, for the triple-layers lap steel structure of the body, which is 1.98~2.47 times of the maximum tensile strength of the resistance spot welding joint, having a significant advantage.