Abstract: As the battery box goes lightweight, suitable lightweight materials are selected to match the panels at different positions of the battery box and take full advantage of material properties. In this paper, the TOPSIS method based on CRITIC weight and orthogonal test is employed. First, the decision-making matrix of the properties of commonly used metal materials in battery boxes is built, and the TOPSIS method based on CRITIC weight is employed to standardize the processing, eliminate the dimensional differences of different groups of data, determine the objective weight of each group of data, calculate the relative fit of each scheme, and select alternative materials. Then, the orthogonal experimental design and range analysis are employed to match the alternative materials with different plates in the battery box, and a multi-material battery box is created. Finally, the size of the multi-material battery box is optimized. The optimized battery box model reduces weight by 5.3 kg with a weight reduction rate of 11.37% while meeting the requirements of strength, stiffness and low-order mode frequency.