Abstract: The resistance spot welding process of the recently developed DH780 dual phase steel with improved formability was studied. The welding process window was obtained by determining the maximum and minimum currents under double-pulse current with three different welding times. The microstructure analysis, hardness test, tensile shear test and cross tensile test were carried out for the spots corresponding to the key process points of the welding process window. The results show that the weld nugget zone experiences melting and rapid cooling and it is transformed into martensite structure.The heat affect zone can be divided into three zones, namely coarse grain zone with coarse martensite structure, fine grain zone with fine martensite structure and partial phase transformation zone with a mixed structure of martensite and ferrite. The hardness of the heat affected zone first increases and then decreases from the nugget side to the base metal side, and it reaches the maximum value in the fine grain zone. The tensile shear force at the left boundary of the welding window is significantly smaller than that at the right boundary. The cross tensile force is similar at different process points. The tensile shear force is significantly higher than the cross tensile force.