Abstract: The Cu₂O/AC catalyst prepared by pyrolysis of copper acetate supported on activatede carbon was pretreated under oxidative (O₂/N₂) or reductive (H₂/N₂ and CO/N₂) atmospheres. The oxidation/reduction of Cu₂O was completed through pretreatment at 350 ℃ for 4 h, the Cu₂O in catalyst could be completely oxidized to CuO by oxidative atmosphere, or reduced to metallic copper by reductive atmosphere. The catalyst activities were evaluated in a continuous fixed-bed tubular micro reactor under atmospheric pressure at 140 ℃. The catalyst pretreated by CO/N₂ had good Cu⁰ dispersion on its surface and exhibited the highest activity. The space-time yield and selectivity of DMC reached 261.9 mg/(g·h) and 74.7%, respectively. After 58 h reaction, the valence state of copper species and the catalytic activity of catalysts pretreated by reductive atmosphere were found to be close to that of the Cu₂O/AC catalyst. Comparing the catalytic performance, the characterization of surface and bulk copper species before and after reaction, it was obvious that metallic copper exhibited a high initial activity, while Cu₂O was stable in catalytic activity and valence state, and CuO was low in activity.