The reasonable design of the vehicle front-end structure stiffness can effectively improve the performance of pedestrian protection. The optimal design of the bumper absorber was completed by structure optimization, and the stiffness curve was the object. The crash test of the bumper of a passenger car was conducted. Meanwhile the finite element model of the collision between the bumper and rigid pillar was established. The accuracy of the finite element model was verified through comparison between the simulation and test results. In order to make the stiffness curve of the bumper area be close to the ideal stiffness curve, the design variables were the geometric shape and the material stiffness of the absorber. The object was to minimize the area between the ideal stiffness curve and the bumper stiffness curve. Adaptive response surface method was used to optimize the absorber. The result shows that the bumper stiffness curve of the optimized material stiffness and geometric shape is consistent with the ideal stiffness curve and meets the requirement of the pedestrian protection.