Abstract: According to the advantages of lightweight, high specific rigidity and strength of the composite material, it has been designed for the light weight of a certain type of electric vehicle battery box structure, which aims at reducing the weight of the electric vehicle. By applying Patran&Nastran as the analysis platform, this study uses the finite element analysis method to compare the bearing capacity of the battery box structures of two kinds of steel and carbon fiber/epoxy composite. Then, a reasonable structure of carbon fiber/epoxy battery box was designed. On the basis of Tsai-wu strength theory, the strength of carbon fiber/epoxy battery box was checked. Results show that the bearing performance of the battery box is not reduced under the condition of reducing the 64% weight of the battery box.