Abstract: The reason for the computational difficulties in the flight vehicle coupled system optimal design is analyzed.The analysis shows that there are two nested iteration loops in the computation of coupled system optimization,that is,the outer loop of the optimization and the inner loop of solving coupled equations.The computational scheme of the nested iterations results in high amount of computation and low accuracy.Based on the analysis,a sequential approximate optimization method is presented.In this method an approximate uncoupled model of the original coupled system is constructed by using the response surface method,and the optimization is then performed based on the approximate uncoupled model.To ensure the accuracy of the approximation,the uncoupled approximate model is refined at each iteration by using the optimum point of previous iteration.A numerical example of an unmanned aerial vehicle(UAV) wing design shows the effectiveness of the presented method.