Abstract: A new secondary passive heat removal system was designed for CPR1000. In order to verify the capability of removing heat for the system under the major feedwater line break (MFLB) accident, the model of the simplified system for CPR1000 was established by using RELAP5/MOD3.2 code. The calculation results show that natural circulation in passive heat removal system is quickly established, and the increasing of temperature and pressure in the primary loop is mitigated due to the timely input of passive heat removal system. There is no bulk boiling in the primary loop and the pressurizer does not overflow before the operator isolates the affected steam generator, which assures the integrity of the core and the main coolant system.