Abstract: By control joining parameters of ultrasonic power (500 W-700 W), welding time (0.5 s-1.5 s) and welding pressure (0.2 MPa-0.5 MPa), ultrasonic spot welding was used to join 0.3 mm thick dissimilar material sheets. The effects of different parameters on the microstructure and mechanical properties of the welded joints were studied. The results show that increasing the ultrasonic power, prolonging the welding time and increasing the welding pressure can promote the flow and mixing of materials at the Al/Cu interface, but excessive ultrasonic power or welding pressure results in the fracture of Cu sheet. Increasing the ultrasonic power promotes the removal of the oxide layers and the material mixing at the bonding interface, and increasing the welding time promotes the material mixing at the bonding interface. The maximum tensile shear load of 510 N is obtained when the ultrasonic power is 600 W, the welding time is 1 s and the welding pressure is 0.3 MPa. Obvious intermetallic compounds are not detected on the fractured surface.