In this work, the Cu single-atom catalysts (SACs) supported by metal-oxides (AlO-Cu, CeO-Cu, and TiO-Cu) are used as theoretical models to explore the correlations between electronic structures and CORR performances. For these catalysts, the electronic metal-support interaction (EMSI) induced by charge transfer between Cu sites and supports subtly modulates the Cu electronic structure to form different highest occupied-orbital. The highest occupied 3d orbital of AlO-Cu enhances the adsorption strength of CO and weakens C-O bonds through 3d-π* electron back-donation. This reduces the energy barrier for C-C coupling, thereby promoting multicarbon formation on AlO-Cu. The highest occupied 3d orbital of TiO-Cu accelerates the HO activation, and lowers the reaction energy for forming CH. This over activated HO, in turn, intensifies competing hydrogen evolution reaction (HER), which hinders the high-selectivity production of CH on TiO-Cu. CeO-Cu with highest occupied 3d orbital promotes CO activation and its localized electronic state inhibits C-C coupling. The moderate water activity of CeO-Cu facilitates *CO deep hydrogenation without excessively activating HER. Hence, CeO-Cu exhibits the highest CH Faradaic efficiency of 70.3% at 400 mA cm.