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• The role of O v on Cu/ZnO catalysts for syngas conversion was revealed by DFT calculations and microkinetic simulations. • The defective Cu 4 /ZnO(0001)-5%O v surface showed better catalytic performance for ethanol formation. • Both of the barriers of CHO and CO coupling and forming C-C-O precursor were lowered because of the existence of O v. • O v promoted the electron transfer between adsorbates and Cu 4 /ZnO(0001) surface. Syngas conversion into methanol or ethanol over Cu/ZnO catalyst has attracted great interest due to its low energy consumption and high value-added. Here, syngas conversion over perfect and defective Cu 4 /ZnO(0001) catalysts were investigated via combining density functional theory (DFT) and microkinetic simulations. Our calculations show a clear change in the reaction mechanism when going from perfect Cu 4 /ZnO(0001) surface to defective Cu 4 /ZnO(0001) with 5% oxygen vacancy (O v) surface. The existence of O v hinders the formation of methanol by increasing the activation barrier of CHO hydrogenation to CH 2 O, but promotes the coupling between CHO and CO and the formation of C-C-O precursors that are favorable to form ethanol. In essence, the surface localized microenviroment charge redistribution owing to the presence of O v adjusts the product selectivity. Detailed Bader charge results for the first time quantitatively identify that O v promotes the electron transfer between adsorbates and Cu 4 /ZnO(0001) surface, and then influences their electrostatic interaction and spatial structure, resulting in syngas conversion into different products. Microkinetic simulations show that the adsorption energies of CO and H on the Cu 4 /ZnO(0001)-5%O v surface has a notable effect on product selectivity. In addition, we verify that the hydrogenation ability of Cu 4 /ZnO(0001) is not well with the presence or absence of O v. [ABSTRACT FROM AUTHOR]