Abstract: By taking account of the random variability of initial underground stress, seepage and material properties of both rockmass and rockbolt, based upon nonlinear stochastic finite element method, a method of reliability assessment is suggested for the safety of undergound structures. By using the method, the excavation procedure can be simulated step by step. The mean value and standard deviation of displacement and stress of both rockmass and rockbolt can also be conveniently obtained. Applications to a practical engineering project are given to demonstrate the suggested method. Some useful conclusions are also obtained.