Abstract: The reactor coolant system simulation model for the two-loop nuclear power plant is established using the thermal hydraulic analysis software Flowmaster. The power operation steady condition, the bias-loop operation steady condition during startup/shutdown reactor, the pump coastdown operation transient condition after loss of off-site power are simulated. The results show that the simulation data matches well with the design values and actual operation values, and the deviations are less than 4%. The simulation model provides a reference for the design optimization and operation of the subsequent reactors of the same type.