To ensure that the air inside the box does not fall below -20 °C after cooling for four hours, With the help of CFD numerical simulation technology, the composition materials and thickness have been optimized and designed in this paper. In this paper, there are two kinds of materials for box wall panel, one is insulation material 1 with smaller specific heat capacity and steel, the other is insulation material 2 with larger specific heat capacity. The simulation analysis results of two types of box wall panels show that the air temperature at edges and corners is difficult to meet the requirements. By using local thickening, this situation can be greatly improved.