Abstract: Resistance spot welding was performed on TC4 titanium alloy and 304 stainless steel sheet with copper foils of different types and thicknesses as transition layer materials. The influence of the type and thickness of the copper foils on the microstructure and properties of the joint was studied. The results show that the shear strength of the welding joint with pure copper foils as the transition layer was significantly higher than that of the copper alloy foils as the transition layer, and the welding joint with T4 copper foil as the transition layer had the highest shear strength. With increasing thickness of the T4 copper foil, the width of the reaction zone of the joint decreased, the width of the intermediate transition zone increased, and the Ti-Fe intermetallic compound in the fusion zone decreased, the shear strength of the joints increased first and then decreased, reaching the maximum when the thickness was 0.4 mm.