Abstract: With the rapid development of new energy vehicles, the connection of the power battery shell has attracted much attention. In order to obtain high-quality welded joints of battery shells, high-frequency induction welding (HFIW) technology was used to weld the battery shell of 3003-H18 aluminum alloy with a thickness of 0.35 mm, and the effect of the welding process on the macroscopic morphology, microstructure, and mechanical properties of the weld was analyzed. The results show that the heat-affected zone of the aluminum alloy after HFIW is small; the width of the weld is extremely narrow; its microstructure is fine isometric crystals without defects such as holes and oxide inclusions. The average grain size is approximately 9.5 μm. With a welding power of 11~12 kW, a welding frequency of 770 kHz, an extrusion amount of 0.15 mm, and a welding speed of 60 m/min, the welded joints with optimal comprehensive mechanical properties can be obtained. The tensile strength reaches 150 MPa, accounting for 70% of that of the base material, and the elongation after fracture is 1%, accounting for 43% of that of the base material. The welded joint hardness generally exhibits a W-shaped distribution. The reasons of decline in the mechanical properties of the joints lie in two aspects. On the one hand, it is related to the large-angle grain boundaries and recrystallization structure. On the other hand, the tensile strength and hardness of the welded joints are also influenced by the size of grains and distribution of the second-phase particles.