Abstract: In this paper, sensitivity study of secondary side passive residual heat removal system on starting mode, heat transfer area and flow resistance has been conducted by RELAP5. The results show that both water-injection starting mode and liquid-column starting mode have little effect on the transient characteristics of secondary side passive residual heat removal system. Compared to the standard condition, at the condition of 37.5% heat transfer area, the discharge flow rate of the makeup tank is relatively increased, and the drain time for the makeup tank is relatively decreased. At the condition of double resistance, the discharge flow rate of the make-up tank decreases, while the drain time is increased by 1000 s.