According to the special requirements of the electric vehicle, a method on the basis of topology optimization and genetic algorithm was presented. In a sample of an electric vehicle, the optimization process includes structural topology optimization and section optimization through topology optimization model, finite element conceptual model, size optimization and manufacture of prototype, which indicates that the forward design can be achieved. In the process of optimization, the objectives are bending stiffness and torsional stiffness, and meanwhile, the minimum weight was set as a constraint. By choosing high sensitive beams, the multi-objective optimization was presented with genetic algorithm. Compared with the results of the real car, this method can meet the requirements of light weight design and manufacture, which provides theoretical significance in increasing the efficiency and accuracy of optimization.