This paper presents an experimental study on the static tensile test of resistance spot weldingbetween 2. 0 mm thick dissimilar 301L?DLT and Q235B in tensile?shear specimens with different welding nugget diameters. Force?displacement curves of the specimens were compared with simulation curves by the finite element software. The stress?strain distribution and fracture evolution process during the tensile process were analyzed. The hardness of the nugget was higher than that of the base material and the heat affected zone. Under static tensile load, the stress and strain in the spot welded joints increased exponentially with the increase of displacement, and the maximum stress was located at the nugget edge of the 301L plate loading side. The static tensile strength and plastic deformation of the spot welded joint failure by the nugget pulled?out fracture mode was better than that by the interface fracture mode. The critical nugget diameter of Q235B for the transition from nugget interfacial fracture to the pull?out fracture was 7.12 mm, and that of 301L was 7.81 mm, which was about 5√ t .