It is proposed to introduce approximate model method to crashworthiness optimization design of thinwall beam,and the approximate model can be optimized by using sequential response surface method.In order to solve the parameterization design problem of finite element model,a parameterization model about material,crosssection size and spotweld of thinwall beam is established by developing corresponding procedures.The results show that optimization design can not only improve the performance of absorbing energy of thinwall beam,but also reduce the weight greatly;the approximate model method can greatly improve optimization efficiency.