Abstract: Fuzzy reliability of a structural system is widely concerned in engineering practices, where the identification of the worst failure mode and the establishment of the corresponding performance equations are two critical issues. In this paper, fuzzy mathematical theory and reliability analysis are combined, thus to evaluate the fuzzy reliability of a structural system whose probabilistic models involve fuzzy variables. Then, the computation models to calculate the fuzzy failure probability of the structural system are established for both correlated failure modes and uncorrelated failure modes. The presented criterion to enumerate the failure modes guarantees the consideration of the worst failure mode. At last, a numerical example is presented to illustrate the application of the proposed method.