Abstract: A rule to determine whether a structure has failed or not in the finite element method (FEM) analysis is proposed in this paper. An example proves that the rule is of high credibility. Based on the rule, the state space of sampling point can be located. A unified method to restructure the performance function called the state space response surface method is built. It is valid when output variable is not continuous while the general response surface is not. The new method takes the difference between the distance from sampling point to failure space and the distance from sampling point to reliable space as the output variable. Numerical simulation experiments show that this method is of universality and precision.