Abstract: With the rapid development of new energy vehicles, the connection of the power battery shell has attracted much attention in the country. In order to obtain high quality welded joints for battery shells, High Frequency Induction Welding (HFIW) technology is used to weld the battery shell of 3003-H18 aluminum alloy with a thickness of 0.35 mm, and the effect of welding process on the macroscopic morphology, microstructure and mechanical properties of the weld is investigated. The results show that the heat affected zone of the aluminum alloy is small after HFIW and the width of the weld is extremely narrow, and its microstructure is fine isometric crystals without defects such as holes and oxide inclusions. With an extrusion amount of 0.15 mm, welding power of 11–12 kW, frequency of 770 kHz and welding speed of 60 m/min, the best mechanical properties of the welded joint can be achieved, tensile strength up to 150 MPa, for the base material tensile strength of 70%, the elongation after fracture of 1%, for the base material elongation after fracture of 43%, the welded joint hardness is generally W-shaped distribution. The large angle grain boundaries and recrystallization structure are primarily responsible for the decline in mechanical properties of the joints; however, the tensile strength and hardness of the welded joints are also influenced by the size and distribution of the second-phase particle size.