By use of the theoretical method of density functional theory (DFT), we systemically investigate the chalcogen doped Cu-4 metal clusters (Cu4O, Cu4S, and Cu4Se) as catalysts for the electrochemical CO2 reduction with toluene as solvent. These doped clusters have efficient catalytic properties which can reduce CO2 to CH4 and a small amount of CH3OH. In the case of CO2 hydrogenation to CH4, the reaction barrier of the Cu4O cluster and Cu4S cluster are reduced by 0.37 eV and 0.15 eV, respectively, compared with the pristine Cu-4 cluster. The calculation results also show the overpotentials for the CO2 hydrogenation to CH4 in the order of Cu4S < Cu4O < Cu4Se. In addition, the geometry structures, the electronic properties, and the reaction free energies on the chalcogen doped Cu-4 clusters are also discussed to further reveal the reaction mechanism in the CO2 electroreduction process. We hope that our present work will enlighten extensive studies on the modified electrode to decrease the limiting potential and provide a reference for the subsequent studies. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.