Abstract: This paper took advanced nuclear power plant (NPP) AP1000 as research object and made a design for passive auxiliary feedwater system (PAFS) on the secondary side of steam generator (SG), of which the auxiliary feedwater pump was driven by steam exhaust. The operation characteristics of PAFS were calculated under station blackout (SBO) accident to analyze the capability of coping with accident by using RELAP5 code. The results indicate that PAFS can remove core residual heat significantly and assure the reactor safety after SBO accident. The pressurizer will be emptied at 170 min later caused by coolant volume shrinkage. The continuous operation time of PAFS is 200 min, which would remove most of core residual heat. PAFS can be used as emergency mitigating scheme for SBO accident.