Abstract: Using ER55-B2-MnV welding wire as filler, argon arc welding was used to weld 15CrMo/Q235B dissimilar steel. The parameters were optimized by controlling variables, and the microstructure and mechanical properties of 12 groups of welded joints with different welding process parameters were studied by combining optical microscope, scanning electron microscope and other equipment. The results show that the welded joint is well formed and has no defects such as cracks and incomplete fusion. The microstructure of welded joint includes martensite, bainite and ferrite, and the metal elements between base metal and weld have migrated and diffused. The hardness of the weld is greater than that of the base metal on both sides, and the change value of the heat affected zone on both sides is relatively small; During the fracture process of tensile specimens at room temperature, the fracture positions are all on the side of Q235B base material, mainly because the bearing area is reduced by dimples with different depths, and the fracture form is ductile fracture. The impact absorption energy in the weld area is the highest, followed by 15CrMo base metal and its heat affected zone, and Q235B base metal is the lowest. The research results provide a certain data basis and theoretical support for the actual production and field application of 15CrMo/Q235B dissimilar steel.