• Designing unique system based on Ag/ZnO/g-C 3 N 4 . • Charge separation and transfer mechanism discussion. • Photocatalytic CO 2 conversion to CO/CH4. Methane and CO have superior economic value and application panorama compared with other products, and these are the ideal products of CO 2 photo-reduction. However, low CO 2 conversion efficiency and poor selectivity are huge obstacles to its practical application. Herein, we develop a three-component photocatalyst hetero-junction of Ag-ZnO/g-C 3 N 4 for superior CO 2 reduction. It is demonstrated that the amount-optimized nanocomposite exhibited exceptional visible-light photoactivities for CO 2 conversion to CO, with ≈ 9-time (36 µmol g −1 h −1 ) enhancement compared to the widely accepted g-C 3 N 4 prepared from melamine as the raw material. Similarly, the silver-modified samples exhibit a considerable increase in methane production, with 14 µmol g −1 h −1 , which is significantly more than the CH 4 production of 2 µmol g −1 h −1 by pure g-C 3 N 4 . Based on the photo-physical data, it is concluded that the coupled ZnO, which accepts electrons and improves reactant adsorption, and the modified Ag, which further promotes the photocatalytic reaction, are much more responsible for the high photoactivities. Moreover, it is suggested based on the photocatalytic experiments with isotopic 13 CO 2 that the produced • CO 2 as active radicals dominated the conversion of CO 2 to CO/CH 4 . This work provides a feasible strategy to design high-performance, low-cost, and sustainable g-C 3 N 4 -based nanocomposite photo-catalysts with a wide range of visible light activity for CO 2 reduction.