Abstract: The transient thermal hydraulic characteristics of CPR1000 were analyzed by using RELAP5/MOD3.4 code to verify the capability of the passive emergency feedwater system (PEFWS) for accident mitigation under the condition of station blackout accident (SBO). The calculation results show that the PEFWS of CPR1000 can supply the water to steam generator immediately and remove the core residual heat after the SBO successfully, and it also shows that the design of the PEFWS of CPR1000 is successful.