During the winding process of aluminum foil used in the lead wire loop,aluminum foil needs to be welded. Because the aluminum foil is extremely thin（about 0.25 mm）,using conventional welding methods such as MAG and TIG will be easy to burn through the base material and is difficult to form an effective welded joint. In this paper,a ultrasonic welding method is used and a complete set of welding technology is selected from the parameters of welding amplitude,welding pressure,welding time and so on. A number of welding samples are made,and the reliability of the welding quality of aluminum foil is comprehensively analyzed by the test methods of welded joint,such as mechanical property,scanning electron microscope and microscopic metallographic test. The results show that the ultrasonic welding of aluminum foil is feasible,and this welding technology can obtain the welded joints that meet the design requirements.