Abstract: The ability of nuclear power plants to deal with Station Blackout (SBO) accident has attracted much attention after Fukushima accident. Whether there is a sufficient ability to mitigate SBO accident has become crucial to measure the safety performance of a nuclear power plant. As a new type of reactor, small modular reactor requires higher safety performance. The mitigating effect of passive residual heat removal system and passive core cooling system for SBO accident of ACP100 is studied in this paper. The results indicate that ACP100 is with multiple strategies to deal with SBO accident that rely little on reliable power supply. Long-term residual heat removal and resultant long-term coolability can be ensured for ACP100 by the residual heat removal system or passive core cooling system.