Abstract: To verify the scheme design of small reactor for China General Nuclear Power Group, especially the scheme design of passive safety injection system, the primary loop, the second loop and the passive core cooling system were modeled based on the RELAP/SCDAPSIM code. The break loss of coolant accidents (LOCA) including equivalent diameter 0.04 m cold leg break, equivalent diameter 0.2 m cold leg break, double-ended direct injection line break, and inadvertent ADS actuation were simulated and calculated. The results show that the primary loop can achieve effective cooling and depressurization, and the core does not become overheat. The safety of small reactor and the rationality of the passive core cooling system are verified.