Abstract: In this paper, the TRACE and SNAP were used to establish twoloop PWR thermal hydraulic system analysis model. The different accumulator design schemes were calculated and analyzed under LBLOCA. The safety injection effect was accessed according to simulation results by comparing peak cladding temperature of each design under LBLOCA. In the end, the possible way to optimize design was found through this study. The research results show that the upper plenum and downcomer injection at the same time is more effective than the cold leg injection or the downcomer injection, and the proper selection of initial accumulator pressure can lower peak cladding temperature and increase LOCA safety margin.