Abstract: This study used the Computational Fluid Dynamics（CFD） program CFX5 to calculate the flow in the hot gas chamber and the hot gas duct in high temperature reactor,on the basis of the experimental research.The calculated results including velocity flow field,pressure field and temperature field were ob-tained,which could be a reference for the design and experimental research of the hot gas chamber of the high temperature reactor.The numerical simulation results indicated that the gases in the hot gas chamber mixed intensively,which accelerated the heat transfer for the gases with different temperatures,and which was in favor of the temperature mixing for high temperature and low temperature gases.In the ribs area,the gas mixing is not so intensive,which had negative effect on the heat transfer between gases with different temperatures.The temperature mixing rate in the hot gas duct increased with the increase of the hot gas duct,and when the length of the hot gas duct was more than 2.5 m,the temperature mixing rate was above 99%.