Syngas to ethanol conversion is getting attention as one of the promising routes to obtain an appealing alternative fuel. A detailed reaction mechanism for ethanol synthesis was constructed on the gamma-Al2O3 (110D) surfaces with different hydroxyl coverages using periodic density-functional theory and a microkinetic model, which provide insights into the influence of surface hydroxyl. We found that with the increasing of hydroxyl coverage, the interaction between CH3 and CO evolves from attraction to repulsion. The formation of CH3 and CH3CO became more facile on the surface with higher theta(OH), which is elucidated by the electrostatic potentials and Bader charge analyses. Moreover, the selectivity of CH3CH2OH can be greatly improved by reinforcing the CO adsorption or decreasing the H-2/CO ratio. Our study could offer distinctive guidance for the preparation of efficient catalysts and broaden the understanding of the mechanism of ethanol synthesis.