A design method is applied for protection load bearing body. Firstly the finite element model of the vehicle body is established. Using the topology optimization technique, the structure of the vehicle body is optimized. In details the first order modal and the stiffness of the body are both improved. Meanwhile the lightweight design of the vehicle is realized in the optimization. Based on the optimal vehicle body, the loads at the connection points of the vehicle body and chassis are obtained using the multi-body dynamics simulation technique. Making use of the loads at the connection points and the FE model, the strength of the vehicle body is analyzed. It proves that the strength of the optimal vehicle meets the requirements. This design method can be also applied for other types of vehicle bodies even other vehicle components.