A finite element collision model was established to simulate the collision between pedestrian's lower leg and a car, and it was verified through experiment. In order to improve the performance of pedestrian protection, auxiliary bumper and energy-absorption foam were added in the car. With taking the thickness of energy-absorption foam, the vertical distance between bumper and auxiliary bumper and the thickness of auxiliary bumper as design variables, an optimized Latin hypercube experiment was conducted. The response surface model (RSM) for the injury index of leg was fit with experimental data by using the least square method, and the optimal design parameter of bumper was solved by multi objective genetic algorithm (MOGA). The results indicate that the injury of the pedestrian leg is reduced effectively by using the optimal structure, which meets the safety requirements.