Abstract: CFD computations were conducted to investigate the effect of different initial temperatures of the AP1000 In-containment Refueling Water Storage Tank (IRWST) on the heat exchange performance of Passive Residual Heat Removal heat exchanger (PRHR HX), and to discuss possible benefits of adjusting the water temperature of IRWST. The standard $k - \varepsilon $ model is selected for the turbulence model and the SIMPLEC algorithm is selected for the correction of pressure and speed. The results show that reducing the initial temperature of IRWST can improve the heat exchange performance of PRHR HX. In addition, the initial temperature of IRWST is directly proportional to the average temperature at the tube bundle outlet. Furthermore, the relative temperature drop at the inlet and outlet of the tube bundle increases linearly with the decrease of the initial temperature of IRWST. On this basis, the following research and development directions are prospected, and the following design thought is put forward: after an accident, first increase the IRWST water temperature to reduce the thermal stress damage and fluid vibration of the core components, and then slowly reduce the IRWST water temperature to maintain the heat exchange capacity, so that it not only keeps the integrity of the reactor core, does not damage the reactor core components, but also can maintain the long-term cooling of the reactor core.