Seismic probabilistic safety assessment(SPSA) is one of the methods for evaluating the safety of nuclear power plants for the seismic event. It consists of the accident sequence and consequence evaluation based on the hazard analysis and fragility analysis to estimate the core damage frequency. In general, analysts develop a primary event tree and secondary event trees in the accident sequence evaluation. The primary event tree considers the seismic fragilities of the major structure, system and component(SSCs). Corresponding to the initiating events, each sequence in primary event tree can be assumed to result in direct core damage or be linked to a secondary event tree for more detailed analysis.