The effects of the addition of Cu to a Fe3O4 catalyst on water-gas shift reactions (WGS) are investigated using first-principle calculations. To elucidate the doping effect, the adsorption of CO and H2O (the reactants in WGS) molecules is studied on the surfaces of pure Fe3O4 and Cu doped Fe3O4. The results reveal that Cu dopants in the Fe3O4(1 1 1) surface are effective in enhancing the adsorption strength of CO molecules as well as in inhibiting excess water molecules from covering active sites. Simultaneously, it is found that Cu dopants improve the activity of the Fe ions adjacent to dopants for adsorbing both CO and H2O. Therefore, it is possible to control the adsorbance of CO and H2O to reach a proper proportion for WGS through changing the concentration of Cu promoters in the catalysts. The mechanism of doping effects is discussed based on the chemical bond theory and Bader charge analysis. Additionally, the co adsorption of CO and H2O is studied on pure and Cu doped Fe3O4(1 1 1) surfaces. The calculated results also suggest that doping of Cu atoms in Fe3O4 would improve the stability of the reactants co adsorbed on catalysts, which is beneficial for the WGS reaction. (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.