In this study, Pd/Al2O3 and Pd-Ru/Al2O3 catalysts were used to investigate the mechanism of the methanol steam reforming (MSR) reaction and the factors affecting the reaction activity. First, the MSR reaction activity was evaluated using Pd/Al2O3 and Pd-Ru/Al2O3 catalysts. The MSR reaction activities increased with the addition of Ru. In addition, FT-IR analysis was performed to investigate the MSR reaction mechanism. The reactions with the Pd/Al2O3 and Pd-Ru/Al2O3 catalysts proceeded through the same mechanism. After methanol was adsorbed on the catalyst surface as methoxy and formate species, it was converted into CO through decomposition and reaction with water, and then desorbed from the catalyst surface. TEM analysis revealed that the addition of Ru to the Pd/Al2O3 catalyst resulted in small particle sizes with highly dispersed Pd on the catalyst surface, which increased the conversion to CO. Lastly, analysis of adsorption characteristics showed that the addition of Ru enhanced the desorption rate of adsorbed CO species to promote the MSR reaction activity by weakening the adsorption intensity of CO. The desorption of CO adsorption species was the rate-determining step of the MSR reaction.