Abstract: Steady-state calculations are performed using RELAP5/MOD3.2 code for a test facility which has the same size as one type of secondary-side passive residual heat removal system. In some conditions there are obvious differences between calculation results and experimental data. Thereby, the steam vertical in-tube condensation models for laminar and turbulent conditions in RELAP5 code are improved by considering the interfacial shear stress between vapor and liquid film and high system pressure, respectively. Steady-state and transient calculations are performed using the improved RELAP5 code for the test facility. The simulation results give a good agreement with the experimental data.