Abstract: The reliable operation of passive core cooling system (PXS) has an important effect on safety of nuclear power plant under earthquake. The FT (fault tree) method was used to calculate the failure probability of each subsystem of PXS with peak ground acceleration (PGA) at 0.5g, 1.5g and 2.5g respectively and the contribution of components to system failure probability. The calculation results were compared with results of seismic margin analysis (SMA) method in “AP1000 Probabilistic Risk Assessment” and the anti-seismic ability of equipment was analyzed. The results show that the conditional failure probability and the contribution of each component to the system failure are in accordance with the results of the SMA method. The method can provide reference for the safety analysis of AP1000.