Abstract: A conceptual design of a passive core cooling system (PCCS) was proposed in order to removal residual core heat during accident scenarios. Strong coupling feedback effect exists between natural convective heat transfer of the PCCS and the temperature distribution within the reactor core, which has a significant impact on the heat removal performance of the PCCS and the peak fuel temperature. An integral computational model dedicated to micro gascooled reactor, which includes both the PCCS and the reactor core, was developed. Comparisons of results predicted by this model and reference results of two benchmark problem, i.e. exercises of MHTGR and natural convection in a square cavity, show a satisfactory agreement, which thus validate the model. Thereafter, in order to explore the operational characteristics of the PCCS proposed in this work as well as the temperature response of the reactor core, and to assess its mitigative performance during accident scenario, this CFD model was then employed to analyze both the steady state under normal operation condition and the pressurized-loss-of-forced-cooling (PLOFC) accident. The calculation results show that the natural circulation of air is steady and regular during normal operation. The heat loss due to the PCCS is acceptably small, which will not lead to significant impact on the core temperature. During the PLOFC accident, the heat removal power of the PCCS is high in the early phase, whereas its performance gradually decreases as the temperature of the reactor vessel decreases in the long term. In general, the PCCS can effectively remove the residual core heat, thus maintaining the reactor integrity. Consequently, the integral CFD model created in this work can be applied to the design and the safety analysis of the PCCS for the micro gascooled reactor.