According to the experience in Probabilistic safety assessment (PSA) studies of operating NPPs, one of the most important external events affecting NPP safety is earthquakes. The seismic PSA evaluates the risks of severe accidents at nuclear power plants (NPPs) caused by seismic events. Now the Seismic PSA model has been developed for the reference plant. In the study, the code was developed using Monte Carlo sampling, and then the uncertainty analysis of component failure probability was carried out in the seismic PSA. It can be found that the component failure probability in seismic has large uncertainty. And for the simultaneous failure of multi-component caused by earthquake, the failure probability was contributed mainly by the stronger component.