The homologous reactions of methanol and higher alcohols synthesis over Mn promoted Cu-Fe catalysts were investigated by in situ DRIFTS, chemical trapping, H-2-TPR, CO-TPD, ICP, and XRD. The results showed that the adsorbed CO on iron carbide would contribute to the production of methylene, which increased the probability of the carbon chain growth in the HAS process. Moreover, the results of in situ DRIFTS indicated that homologous reaction of methanol, during which process methanol was oxidized to generate formate species which could be inserted by methylene and resulted in the formation of the acid and anhydride species with more cabon atoms and finally led to the formation of alcohols, existed in the HAS process and will apparently affect the synthesis of higher alcohols. Furthermore, the appropriate addition of Mn could facilitate the carbon chain growth and increase the selectivity to C-2(+) alcohols on a Cu-Fe based catalyst.