The solar‐driven CO2 reduction is a challenge in the field of “artificial photosynthesis”, as most catalysts display low activity and selectivity for CO2 reduction in water‐containing reaction systems as a result of competitive proton reduction. Herein, we report a dinuclear heterometallic complex, CoZn(OH)L1(ClO4)3 (CoZn), which shows extremely high photocatalytic activity and selectivity for CO2 reduction in water/acetonitrile solution. It achieves a selectivity of 98 % for CO2‐to‐CO conversion, with TON and TOF values of 65000 and 1.8 s−1, respectively, 4, 19, and 45‐fold higher than the values of corresponding dinuclear homometallic CoCo(OH)L1(ClO4)3 (CoCo), ZnZn(OH)L1(ClO4)3 (ZnZn), and mononuclear CoL2(CH3CN)(ClO4)2 (Co), respectively, under the same conditions. The increased photocatalytic performance of CoZn is due to the enhanced dinuclear metal synergistic catalysis (DMSC) effect between ZnII and CoII, which dramatically lowers the activation barriers of both transition states of CO2 reduction. In sync with zinc: A dinuclear heterometallic CoZn catalyst shows much higher photocatalytic activity than the corresponding dinuclear homometallic CoCo and ZnZn catalysts, or the mononuclear Co and Zn catalysts for CO2 reduction under the same conditions. The high performance of the CoZn catalyst is due to the enhanced dinuclear metal synergistic catalysis (DMSC) effect between ZnII and CoII.