Abstract: Aiming at the requirements of weight loss of the battery box structure for new energy electric vehicles, AZ31 magnesium alloy plate was used to manufacture the power battery box by plasma welding. The microstructure and properties of the welded joints were investigated, and the life of the welded box under loading was simulated and evaluated through ANSYS software. The results show that the weld microstructure of the AZ31 magnesium alloy is α-Mg solid solution andβ-Mg₁₇Al₁₂ precipitated around the grain boundaries in dot shape. The mean microhardness of the AZ31 weld zone is 70.3 HV,and the mean tensile strength of the welded joint is 185 MPa, which reaches 82% of the base metal. The fracture mode of the joint exhibits brittle fracture. The simulation results show that the stress and deformation of the welded joint and the internal baffle of the box are bigger than those of the box at the bottom. The life of the battery box is 1.335×10⁶-8.994×10⁷ cycles under the load of 101-147 MPa, which can meet the daily use requirements of vehicle battery box.