Abstract: The lightweight design of a steel suspension control arm was carried out. A sandwich control arm combined with carbon fiber reinforced plastics (CFRP) and aluminum alloy was proposed. The structure-material integration design was carried out to tap its lightweight potential. Firstly, based on the multi-scale theory of composite materials, the micro, meso and macro cross-scale analysis of CFRP was carried out, and then the mechanical properties of CFRP samples were tested to verify the accuracy of multi-scale analysis. The sandwich control arm including CFRP panel and aluminum alloy core layer was designed, and the structure of aluminum alloy core layer was determined by topology optimization. On this basis, based on the method of approximate model and multi-objective genetic algorithm (NSGA-II), the multi-scale parameters of CFRP and the size parameters of aluminum alloy sandwich layer were selected as design variables. Considering the influence of structural vibration characteristics, strength and stiffness, the cross-scale multi-objective optimization was carried out with the goal of minimizing the mass of the control arm and maximizing the longitudinal stiffness. The entropy weight TOPSIS method was used to mine the optimal solution in the Pareto frontier solution set of multi-objective optimization. The results showed: compared with the steel control arm, the mass of the optimized control arm is reduced by 46.6 %, and other properties are significantly improved, which provides a reference for the structural-material integrated design of the control arm.