A series of unsymmetrical bis(imino)pyridylcobalt complexes was investigated by DFT-QEq method to correlate the net charges of cobalt center and their catalytic activities. The effective net charge values on cobalt atom, calculated by QEq method at doublet spin state, reflected the influences of substituents within their ligands. The catalytic activities of these cobalt complexes in ethylene polymerization continuously increase along with higher values of the effective net charges on cobalt atom. The energy differences at doublet and quartet states kept the constant tendency for the cobalt complexes without the steric influences of substituents within ligands. (C) 2014 Elsevier B.V. All rights reserved.