Abstract: Based on one-dimensional governing equations, the mathematical models of the reactor primary coolant system and the passive residual heat removal system (PRHRS) were established. A dynamic simulation program PRHRSDSC was developed to analyze the transient characteristics of the system. The program was used to simulate the transient process of PRHRS during station blackout accident. The calculated results were compared with LOFTRAN code. The results show that the core residual heat can be removed efficiently using natural circulation to keep the coolant at sub-cooled state and the peak pressure is below the limit of the operation pressure. The parameter variation trends are well consistent with LOFTRAN code and the rationality of the model is demonstrated.