Employing density functional theory (DFT) together with periodic slab models, the adsorption and dehydrogenation of H2O on clean and oxygen-covered Au (1 0 0) have been investigated systematically. Onthe basis of the theoretical analysis, the favorable adsorption sites and stable configurations of all species were clarified. H2O was predicted to adsorb weakly on the top, bridge, hollow sites, with the top site preferred. Whereas OH and atomic O prefer to adsorb on the hollow site and H occupies the bridge site. What's more, this work displayed the optimum configurations for the relevant co-adsorption groups. The results elucidated that co-adsorption is apt to impair the interaction of adsorbate-substrate due to the joining of oxygen atom except for H2O molecule. Eventually, the interrelated transition states and activation energies were calculated to explore the dehydrogenation mechanism of H2O. A feasible mechanism on oxygen pre-covered surfaces for complete dehydrogenation of H2O was also presented. It was illuminated that atomic oxygen could diminish the barrier energy substantially of the first dissociation step and play a pivotal role in the decomposition of H2O molecule. (C) 2014 Elsevier B.V. All rights reserved.