The 3D model was simplified by Abaqus software, and the finite element model of the frame molding die was established by using solid element and shell element respectively, and the stress level and deformation of the mould under the typical working conditions such as bracing, paving and lifting were analyzed. It is found that the difference between the two model analysis results is small, so the shell element can be used instead of the solid element in the lightweight design. Based on the shell elements, the lightweight design of the mould was carried out by using the sizing optimization module of Abaqus, and the suitable thickness of the clapboard is determined.