Abstract: Passive reactor cavity cooling system (RCCS) is an important safety related facility for high-temperature gas-cooled reactor pebble-bed module (HTR-PM). This system is responsible for cooling and protecting the reactor cavity and reactor pressure vessel (RPV). Without any active equipment or human intervention, RCCS can passively remove reactor cavity heat to the ultimate heat sink (atmosphere) by radiation, convection and natural circulation. Considering the safety redundancy, RCCS is divided into three independent units. According to the design requirements of HTR-PM, two units can fulfil the heat removal capacity. In normal operation and accident conditions, about 500 kW and 1 200 kW of heat is needed to be removed respectively. Moreover, the concrete temperature should be controlled below 175 ℃ in accident conditions. Therefor, accurately predicting the heat removal power from RPV to RCCS is important for its thermal hydraulic design. Based on the measured RPV wall temperature distribution during the commissioning of HTR-PM, computational fluid dynamics (CFD) method was used to perform a three-dimensional full-scale simulation of the convection and radiation heat transfer between RCCS water-cooling wall and RPV. The numerical results verify that Realizable k-ε turbulence model and discrete ordinates radiation heat-transfer model can accurately predict the heat removal power of RCCS, with a relative error of about 10%. In normal operation, only one unit of RCCS can remove the heat power greater than 500 kW. Under accident condition, two units of RCCS can remove the heat power of about 1 200 kW. As for the temperature distribution of its water-cooling wall, the maximum temperature difference in the transverse direction is about 33 ℃. Furthermore, the effect of cooling water temperature on the heat removal power of RCCS is evaluated in the case of two units of RCCS in operation. For accident condition, when the cooling water temperature increases from 10 ℃ to 100 ℃, the heat removal power can reduce by 380 kW, i.e., it decreases from 1 288 kW to 906 kW. The concrete temperature is always below 105 ℃, which is lower than the design limitation. In summary, RCCS meets the heat removal requirements of HTR-PM, which can effectively cool and protect the reactor cavity and RPV under both normal and accident conditions.