Abstract: In this paper, the passive residual heat removal system (PRS) on secondary side of HPR1000 nuclear power plant is taken as the research object, and the suitability of applying RELAP code to PRS analysis is evaluated. Firstly, by identifying the key phenomena and sorting out program functions, it shows that RELAP code related mathematical model can meet the needs of PRS analysis. At the same time, the applicability of the model was quantitatively evaluated by modifying the heat transfer model of steam condensation in horizontal/vertical tubes in RELAP program and comparing with the results of PRS test bench. On the basis of the above work, the transient process of PRS operation under SBO condition is analyzed by using RELAP. The results show that PRS can establish natural circulation and effectively discharge heat. Finally, the transient condition of PRS misoperation is analyzed. The results show that the reactor is safe under the misoperation condition of PRS, and the design of PRS system meets the requirements.