Abstract: A new passive residual heat removal system (PRHRS) on the secondary side of the steam generator was designed for CPR1000, which can remove residual heat in the core by natural circulation in the secondary side of steam generator and ensure core safety under accident conditions. The model of the simplified system for CPR1000 was established by using RELAP5/MOD3.2 code, and the transient characteristic of PRHRS was simulated under the station blackout (SBO) accident. The sensitivity analysis was performed for the related parameters which affect the working characteristics of PRHRS, such as the volume of high-level tanks, area of heat exchanger, height difference of cold and hot centers and the initiating time of PRHRS. The calculation results show that increasing volume of high-level tanks and area of heat exchanger helps to remove residual heat of the core; but reducing height difference of cold and hot centers has little influence on the capacity of natural circulation for PRHRS; the earlier the initiation of PRHRS is, the higher the water level in the secondary side of steam generator is, the better the PRHRS removes residual heat in the core.