In this paper ANSYS Workbench platform is used for static and dynamic finite element analysis of the battery pack enclosure, and the weak position of the box structure is obtained. The box is Optimized by the topography and composite material optimization, The optimum geometric parameters and plane layout of the convex hull on the box cover are obtained by topography of the Optistruct software, final the three-dimensional model of the optimized upper cover is established. The thickness distribution and optimal thickness of each layer in the lower box is obtained by the composite material optimization. After verification, the maximum deformation of the box after optimization is 82% lower than that before optimization, the stiffness is significantly increased, the maximum equivalent stress is reduced by 70%, and the box strength is significantly improved. The first-order natural frequency is 32.5Hz, which can avoid resonance, the box weight is reduced by 67. After optimization the battery pack box can play more effective protective role for the safe operation of the power battery, and the weight reduction effect is significant, the research lays the foundation for further analysis of the actual battery box structure.