Efficient photocatalytic reduction of CO2 into value-added chemical fuels has been a thorny, challenging and long-term project in the environmental/energy fields due to the low efficiency, especially in the inorganic aqueous environment. In this report, we present a facial approach to modify CdS with Co(II) species through controlling decarboxylation of the Co-EDTA precursor for improved CO2 reduction. Performance evaluation and microstructure characterization reveal that the resulted tetra-coordinated Co(II) modified CdS exhibits the most optimized CO evolution rate of 9.8 mu mol h(-1) (i.e., 392 mu mol h(-1) g((catalyst))(-1) with TOF of 7.94 h(-1)) in aqueous solution under visible light, where the competitive hydrogen evolution reaction is significantly inhibited. Further investigation implies that the fully utilized Co(II) active sites, the tetra-coordinated Co(II) species, the favorable interaction between CO2 and Co(II) sites and efficient charge transferring ensured the high efficiency and improved selectivity. This work would provide a good strategy for the structure engineering of catalytic site to improve photocatalytic CO2 reduction.