The oxidation state of Ga, In and Ag active sites for the selective electrochemical conversion of CO2 to CO has been successfully modulated through the construction of a porous Ga-Ag9In4 liquid alloy catalyst. X-ray photoelectron spectroscopy measurements confirmed the formation of a higher amount of oxidized states on the high-performing Ga-Ag9In4 electrode surface during the CO2 reduction reaction process. Based on density functional theory calculations, the Ga-Ag9In4 catalyst with a high oxidized species exhibits an electronic-rich surface that promotes CO2 adsorption and activation. In a H-type electrolysis cell, the porous Ga-Ag9In4 catalyst exhibits a maximum Faradaic efficiency of 88 % for CO production, with current densities of 30.2 mA·cm−2. This strategy of porous liquid alloy engineering and oxidation state modulation in multicomponent systems has good application prospect and research value for enhancing electrocatalytic performance.