Abstract: DP780 duplex stainless steel with thickness of 2.0 mm was welded by resistance spot welding, relatively good welding parameters were obtained by the welding quality testing, and the microstructure, shear force and microhardness of the spot welded joints were studied. The results show that the relatively good process parameters were the welding pressure of 5 kN, welding current of 9-10.5 kA, welding time of 320-400 ms. Under the relatively good welding process conditions, the fusion zone of the joint was mainly martensite and the heat affected zone was composed of martensite, ferrite and bainite. When the welding current was 9.5 kA, welding time was 400 ms, welding pressure was 5 kN, the shear force and the nugget diameter were the biggest, and they were 32.58 kN and 7.9 mm, respectively. At the same spot welding time and pressure, the microhardness of the fusion zone decreased with the increase of welding current.