Abstract: Aluminum/copper dissimilar joints are widely used in electronics, the automobile industry, and battery manufacturing. Ultrasonic spot welding (USW), as a quality, efficient, clean, and low-consumption solid phase bonding (SPB) technology, is applicable for the connections of aluminum/copper and other highly conductive and heat-conducting materials. At present, this technique has been applied by automobile producers and lithium battery manufacturers at home and abroad. In this work, the optimal performance of the ultrasonic welding process of aluminum/copper dissimilar joints was studied. Based on a single-factor test on how welding parameters (lap mode, welding pressure, welding amplitude, and welding energy) influence the quality of welding joints, the lap mode of aluminum plates on the top and copper plates on the bottom (Al/Cu) was deemed better than that of copper plates on the top and aluminum plates on the bottom (Cu/Al) under the same optimal parameters (40 psi, 45 μm, and 500 J). With this group of parameters, the Al/Cu joint formed a cladding mechanical occlusion. The element had a diffusion layer of 2 μm and a joint specimen maximum failure load of 605 N. © 2020, Pleiades Publishing, Ltd.