Response　surface　methodology　(RSM)　is　a　method　to　solve　sensitivity　of　objective　and　constraints　approximately　in　structural　optimization.　The　errors　between　the　fitting　values　and　the　structural　responses　at　the　design　points　will　affect　the　precision　of　optimization.　This　paper　provides　an　improved　method　that　fit　accurately　at　some　design　point.　Two　numerical　examples　illustrate　its　feasibility　and　efficiency.