Based on density functional theory, together with COSMO (conductor-like solvent model) in Dmol(3), the solvent effects on both the Cu2O(1 1 1) surface properties and the adsorption of CO on Cu2O(1 1 1) surface have been systematically investigated. Different dielectric constants, including vacuum, liquid paraffin, methylene chloride, methanol and water, are considered. The solvent effect on Cu2O(1 1 1) surface properties shows that the solvent favors Cu2O(1 1 1) surface area growth. The adsorption of CO on Cu2O(1 1 1) surface indicates that the structural parameters and adsorption energies of CO are very sensitive to the COSMO solvent model. Solvent effects can effectively improve the stability of CO adsorption on Cu2O(1 1 1) surface and the case of C-O bond activation. The interaction of solvent molecules with Cu2O(1 1 1) surface is compared with that of CO with Cu2O(1 1 1). Results suggest that the solvent effect is the dominating cause for the interaction of CO with Cu2O(1 1 1) surface in solvent, in which Cu2O(1 1 1) shows higher catalytic activity for CO activation. But the solvent may be not the only reason promoting CO activation. These analyses give us some new insights into the understanding of solvent effects. (C) 2011 Elsevier B.V. All rights reserved.