A numerical-simulation method is developed to calculate seismic reliabilities of structures subjected to non-stationary earthquake load with uncertain spectral density in this paper.First,the numerical solutions of the structural unconditional seismic reliability are given from Gauss's integration.Secondly,conditional seismic reliabilities in the numerical solutions at Gauss points are estimated by Monte Carlo simulations.Finally,the unconditional structural seismic reliabilities are calculated by combining the numerical solution and the obtained conditional reliabilities.Numerical results of a single-degree-of-freedom(SDOF) system are compared with that from the plain Monte Carlo simulation, which demonstrates the accuracy and efficiency of the numerical-simulation method.