Abstract: The composite material of stainless steel foil/copper foil has good mechanical properties, corrosion resistance and conductivity. However, due to the large difference in hardness between the two metals, it is difficult to directly perform composite connection. Ultrasonic welding of multilayer stainless steel foil/copper foil was carried out with aluminum foil as the interlayer.The effect of welding energy consumption on the microstructure and mechanical properties of the welded joint interface was studied. The results show that there is no crack in the joint of multilayer composite foil. The atomic diffusion layers with certain thickness are formed at the SS/Al and Al/Cu interfaces, indicating that a certain diffusion metallurgical bonding is realized. The softening and plastic flow of aluminum foil promotes the coordinated plastic deformation between different metals, and mechanical engagement is achieved at the interface.The peel strength test results show that the bonding strength of different interfaces of multilayer composite foil is different. The maximum peeling force of the interface reaches 145 N, and the welding energy consumption is 1000 J at this time.The nano-indentation test results of the joint interface show that the hardness of the side near the welding head is higher than that of the side far from the welding head, indicating that the plastic deformation degree of different layers of foil at the interface is different.