Abstract: Being Taken SUS301 L stainless steel for rail vehicle as the research object,the effect of external magnetic field on nugget size,tensile strength and microstructure of stainless steel spot welded joint was studied. The results show that under the action of external magnetic field,the nugget diameter of stainless steel spot welded joint increases obviously,and the tensile strength increases. The higher the magnetic field strength,the longer the action time,the more obvious the effect of performance improvement. At the same welding parameters,the maximum tensile strength,width-height ratio,pit and nugget structure of magnetron resistance spot welded joint are 16. 7%,47% and 62% higher than those of the common spot welding. Additional magnetic field during spot welding can effectively improve the properties of stainless steel resistance spot welded joint.