Abstract：An improved response surface method，i. e.，the first order reliability method(FORM)-response surface method(RSM) is proposed. This new method can overcome the shortcomings of RSM，which is based on the iteration of response surfaces fitting(RSF). The first step of this method is to calculate the reliability index and the design point by using first order reliability method (FORM)，and the derivatives of limit state function can be gained by finite difference method (FDM) or rational polynomial technique (RPT)，which does not need the explicit expression of the limit state function. Then，a response surface can be fitted on the design point and the reliability index can be calculated by using FORM，and second order reliability method (SORM ) or Monte Carlo simulation method (MCSM) based on this RSF. Therefore，only one RSF is needed in this method. The accuracy and efficiency of this method are better than those of the general used RSM，which are validated by three examples.
