Abstract: Thorium-based molten salt reactor (TMSR) is a kind of fourth generation reactors which uses graphite coated particles as fuel and molten salt as coolant. The fuel pebbles at the reactor core increase the complexity of thermal-hydraulic analysis of the reactor. In order to simulate the temperature distribution of the reactor when the reactor loses forced circulation, modeling and simulation of the reactor core using CFD code are necessary. The TMSR reactor core was simulated using a simplified porous medium model. Mainly considering the heat conduction, buoyancy and insulation layer thickness, a preliminary analysis was completed for the temperature distribution of the reactor during the steady state operation and the 60 s transient after the loss of forced circulation. The results were compared with the simulation results of RELAP5-3D, which indicates the feasibility of using CFX porous medium model for the thermal analysis of the TMSR core, and proves that the molten salt will not boil in the simplified model and boundary conditions.