Abstract: The current status of quantification method and tools for seismic probabilistic safety assessment (PSA) in nuclear power plants was discussed, and the challenges faced by quantitative tools and the issues need to be resolved was suggested. A quantitative method based on the nature of probability theory was proposed. The application process of the calculation method was demonstrated, taking the results of multi-plan probabilistic seismic hazard analysis (PSHA) and the minimum cut set given by the seismic response analysis of a nuclear power plant in China as inputs, and then  the effect of ground motion parameters and confidence parameters on the quantitative results was analyzed. The results demonstrate that the Latin hypercube sampling for the confidence parameter can give a stable estimate of the core damage frequency caused by earthquake (SCDF) in the nuclear power plant even the number of samples is small; in general, the equipment failure contributes the most to the SCDF; the impact of structure failure is relatively small; the contribution of the annual occurrence frequency of ground motion parameter to SCDF needs to be specifically analyzed according to the location of the project site.