Thermal propulsion system includes solar thermal propulsion and nuclear thermal propulsion, and it is a significant issue to improve the heat transfer efficiency of the thermal thruster. Based on the fluid-solid coupled heat transfer, this study utilized the platelet heat transfer characteristics to simulate the heat transfer and flow field of the platelet passage. A coupled system included both the coupled flow and the heat transfer between fluid and solid parts, in addition to the coupled heat transfer among solid parts. Simulation result shows that the fluid-solid coupled method can solve the steady heat transfer in the platelet structure, and the propellant can be heated to the design temperature of 2300K for the thermal propulsion system. 