In a stationary fuel cell system, secondary reformer is utilized to enhance system efficiency. Since the heat sources of stationary fuel cell has low temperature, the operation philosophy of secondary reformer has to be differed from high temperature reformer. Researches on methane steam reformers have been made in various directions, but most have been done only in high efficiency systems. In this study, the design of the steam reformer with the low temperature gas as the heat source would be improved and the temperature distribution would be improved. To do this, computational analysis was carried out. Through computational analysis, we tried to improve radial flow uniformity and temperature distribution of methane and water vapor mixture in the reformer. In order to improve the flow and temperature distribution inside the reformer, the analysis was carried out considering the presence of the spiral vortex generator, the shape of the perforated plate, and the baffle. As a result, the uniformity of the flow was increased by installing the spiral vortex generator, and it was confirmed that the average temperature was increased by installing the perforated plate and the baffles. And an endothermic chemical reaction inside the reaction part and investigated the reforming characteristics according to the temperature and s/c ratio in order to consider the chemical reaction side with the improved structure in the flow side. The s/c ratio was set to 2 and 3, and the temperature was set to 1000K and 1100K. As a result, it has been concluded that the modification of the reforming reaction depends on the temperature and s/c ratio, and additional structural improvement is required.