Copper-based catalysts have been attracting increasing attention for CO electroreduction into value-added multicarbon chemicals. However, most Cu-based catalysts are designed for ethylene production, while ethanol production with high Faradaic efficiency at high current density still remains a great challenge. Herein, Cu clusters supported on single-atom Cu dispersed nitrogen-doped carbon (Cu/Cu-N/C) show ethanol Faradaic efficiency of ∼40% and partial current density of ∼350 mA cm. Quasi X-ray photoelectron spectroscopy and operando X-ray absorption spectroscopy results suggest the generation of surface asymmetrical sites of Cu and Cu as well as Cu clusters by electrochemical reduction and reconstruction during the CO electroreduction process. Density functional theory calculations indicate that the interaction between Cu clusters and the Cu-N/C support enhances *CO adsorption, facilitates the C-C coupling step, and favors the hydrogenation rather than dehydroxylation of the critical intermediate *CHCOH toward ethanol in the bifurcation.