The microstructure and mechanical properties of Mg/Al alloy dissimilar metal resistance lap joints were studied by adding an interlayer of titanium foil. The research results show that adding a 0.2mm thick titanium interlayer can greatly increase the strength of Mg/Al dissimilar metal resistance spot welding joints. The maximum tensile shear force of the joint first increases and then decreases with the increase of welding current.; The maximum tensile shear force reaches the maximum of 2.2kN while the welding current is 14kA. TiAl3 is formed at the aluminum-titanium interface, and the joint fractures in the heat-affected zone on the magnesium side. After conversion, the shear strength of the joint can reach 156MPa. Through SEM and EDS analysis, the addition of a titanium interlayer blocks the mutual diffusion of magnesium alloy and aluminum alloy, and the titanium interlayer hinders the formation of Mg-Al intermetallic compounds, thereby greatly improving the bonding strength of the joint.