Abstract: The configuration parameters of the passive residual heat removal system (PRHRS) were designed according to natural condition of integral pressurized water reactors (IPWRs). By means of the RELAP5/MOD3.4 code, the thermal-hydraulic behaviors effect factors of the system were analyzed and the system was optimized. The numerical results show that the larger the residual heat exchanger (RHE) heat transfer area is, and the higher the height difference between the steam generator and the residual heat exchanger is, the easier the establishment of the natural circulation in the third loop is, but at the same time the higher the peak value of the secondary loop pressure is. According to delaying the steam valve closure time and setting the compensating water tank, which is parallel connected to the RHE, the higher peak value of the secondary loop pressure can be lightened. In the case of satisfying configuration and safety, PRHRS has stronger condensation capability.