Abstract: The in-containment refueling water storage tank (IRWST) is an important part of the passive residual heat removal system of AP1000. In order to evaluate the residual heat removal capability of AP1000, it is necessary to build a suitable model for IRWST and its heat exchanger. However, there is no common method yet to model the refueling water tank and its heat exchanger. In this work, the three-dimensional IRWST heat exchanger was simplified to one-dimensional model with two different system analysis softwares (RELAP5/SCDAPSIM mod3.4 and COSINE). With the support of Major National Science and Technology Projects, the scaled-down AP1000 separated-effects IRWST passive residual heat removal heat exchanger (PRHR HX) test facilities were built in North China Electric Power University to investigate the thermal hydraulic behavior after residual heat removal accident. In this paper, four typical boiling experiment conditions were simulated in above two system analysis softwares with single channel and multi-channel models respectively. The temperature distribution and boiling time of tank were studied under different initial experimental conditions, such as different initial water temperatures, heating power and initial water levels. It is shown that the computed temperature with RELAP5 single channel model and multi-channel model are lower than the measured values, and with the development of natural convection, subcooled boiling and pool boiling, the error increases gradually. In the later stage of the heat transfer process, the consistency between the calculation results of the multi-channel model and the experiment is better than that of the single channel model. The computed temperatures with COSINE single channel model and multi-channel model are higher than the measured values, and the calculation accuracy of the two softwares is equivalent. The calculated overall boiling time with RELAP5 software is later than the experimental time, and the calculated boiling time with COSINE software is generally earlier than the experimental time. Compared with single channel model, multi-channel model takes the transverse cross flow between different channels into consideration, which can improve the overall heat transfer efficiency and shorten the overall boiling time. In the modeling process of system safety analysis, the specific modeling strategy can be determined according to the influence on safety response of the temperature and the overall boiling time from the perspective of conservatism.