First-principle calculations based on the density functional theory (DFT) were used to clarify the influence mechanism of H2S on the reactivity of Ni-based oxygen carriers. A systematic investigation about the adsorption behaviors of H2S on NiO(001) perfect and defect surface was firstly performed. H2S molecule is very likely to produce the sequential dehydrogenation reaction on NiO(001) defect surface, while this phenomenon was not observed on NiO(001) perfect surface. Then the mechanism of CO adsorption on the H2S pre-adsorption NiO(001) perfect and defect surface was clarified. It was revealed that the existence of H2S could notably restrain the CO adsorption process on NiO(001) surface. The H2S influence on the diffusion of the O anion in the NiO slab was also studied in detail. Results showed that the presence of H2S would lead to the higher thermodynamic driving force required for the O anion diffusion, limiting the rate of the diffusion. (C) 2016 Elsevier B.V. All rights reserved.