Abstract: This paper takes the turbine in Ling’ao phase I nuclear power plant as a prototype, and details the numerical model of the turbine based on RELAP5. The calculation under the stable operation condition at 100% power indicates that the detailed turbine numerical modeling remedies the larger calculation error for the enthalpy values by simplified modeling. The detailed turbine numerical modeling is incorporated in the thermodynamic system model for the whole nuclear power plant to conduct the transient analysis, and comparison with the data curves under the step power change from 97% to 87% of the turbine load in the original test report is carried out. The results showed that the error between the enthalpy calculation value for the steady-state model and the actual value of the plant is within 2%, and the analysis parameters for the transient model are in line with the actual situation of the nuclear power plant.