Abstract: Although high power ultrasonic spot welding(USW) can obtain better welding quality about highly conductive materials, the welding mechanism is still unclear. To improve the understanding of the USW process and to enhance the weld strength in similar Cu/Al welding, the effect of clampling force, welding time, vibration amplitude and profile of the sonotrode tips on the temperature rise, intermetallic compound (IMC) growth of welding interface and mechanical properties of joint during Cu/Al high power ultrasonic welding process are investigared. Increasing of clampling force, the thickness of the IMC first increases and then decreases. The interface temperature decreases and the thickness of the IMC decreases linearly with vibration amplitude. The optimal number of welding head teeth is 9. Increasing and decreasing the number of sonotrode teeth will lead to lower interface temperature and formation of welding cracks. In order to obtain high welding quality of Cu/Al joint, the vibration amplitude sholud be set to its maximum. Scanning electron microscopy (SEM) test is performed on the fracture of the Cu/Al joint and shows that the fracture of Cu/Al ultrasonic welded joint is ductile-brittle hybrid mode. The research results provide guidance for optimizing the ultrasonic welding parameters.