At present, there are a variety of methods to solve the uncertainty propagation for engineering structures under various uncertainties.Further, the development of reliability theory promotes the advance of computational technique of structural reliability analysis and risk evaluation [1].In the practical reliability analysis of engineering structures, we often make use of FORM (first order reliability method) and SORM (second order reliability method) in view of searching for the design point (or most probable point) of explicit or implicit limit state function.This kind of method based on design point has simple principle, and in most cases it can satisfy the need of engineers.