Developing　artificial　enzymes　with　excellent　catalytic　activities　and　uncovering　the　structural　and　chemical　determinants　remain　a　grand　challenge.　Discrete　titanium-oxo　clusters　with　well-defined　coordination　environments　at　the　atomic　level　can　mimic　the　pivotal　catalytic　center　of　natural　enzymes　and　optimize　the　charge-transfer　kinetics.　Herein,　we　report　the　precise　structural　tailoring　of　a　self-assembled　tetrahedral　Ti4Mn3-cluster　for　photocatalytic　CO2　reduction　and　realize　the　selective　evolution　of　CO　over　specific　sites.　Experiments　and　theoretical　simulation　demonstrate　that　the　high　catalytic　performance　of　the　Ti4Mn3-cluster　should　be　related　to　the　synergy　between　active　Mn　sites　and　the　surrounding　functional　microenvironment.　The　reduced　energy　barrier　of　the　CO2　photoreduction　reaction　and　moderate　adsorption　strength　of　CO*　are　beneficial　for　the　high　selective　evolution　of　CO.　This　work　provides　a　molecular　scale　accurate　structural　model　to　give　insight　into　artificial　enzyme　for　CO2　photoreduction.