In order to obtain a robust dissimilar joint between titanium and aluminum alloy, a method of resistance spot welding with a cover plate were used to weld two kinds of material. The interfacial microstructure was observed using transmission electron microscopy. The effects of welding parameters on the mechanical properties of the joint were investigated. An approximately 160 nm thick layer of Al solid solution supersaturated with Ti was observed at the welding interface, in which contain the precipitates TiAl3. Mechanical property analysis suggests that the reaction layer has no effect on the tensile shear load of the joint.