Abstract: The model of level 1 probabilistic safety assessment (PSA) of Xi’an Pulsed Reactor (XAPR) was established for internal initial event at 2 MW full-power operation, and the initial event identification, accident sequence analysis and reliability data processing were studied. The quantitative analysis of core damage accident sequence was performed at Risk Spectrum software platform by using small event tree and large fault tree methodology. The results show that the core damage frequency (CDF) caused by internal initial event is about 4.14×10^-6/(reactor•year) for XAPR. Large LOCA at reactor core height is the most important event leading to core damage, and the dominant accident sequence for the CDF is large LOCA at experimental hole, combined with the emergency pumping system failure. The final result confirms the relative high safety characteristics of XAPR.