Methanol synthesis from CO2 and CO/CO2 hydrogenation was carried out under real reaction conditions over an ultrafine Cu/ZnO/Al2O3 (Cu/Zn/Al=60/30/10, molar ratio) catalyst. The formation and variation of surface species were recorded by in situ FT-IR spectroscopy. The mechanisms of methanol synthesis and RWGS reaction were discussed. The result revealed that methanol was formed directly from CO2 hydrogenation for CO2/H-2 Or CO/CO2/H-2 reaction systems. b-HCOOs- was the necessary intermediate for methanol synthesis. A scheme of methanol and RWGS reaction was proposed.