"This paper describes the Thermal Analysis on the reactor for carbon dioxide reduction using porous catalyst. The temperature inside the reactor is high enough for the temperature of the reactor to influence the reduction efficiency, so that it is important to estimate the difference between the temperature on the ground and that on the orbit. But, some problems are known to be difficult to take the thermal characteristics of the catalyst into analytical consideration owing to the irregularity such as the geometry of the porous catalyst and the subsequent flow pattern. In this paper, we make suggestions regarding the modeling of the porous catalyst to estimate the temperature inside the reactor in a ‘mixed temperature’point of view between the catalyst and the reactive flow."