Graphitic carbon nitride (g-C₃N₄, CN) exhibits inefficient charge separation, deficient CO₂ adsorption and activation sites, and sluggish surface reaction kinetics, which have been recognized as the main barriers to its application in CO₂ photocatalytic reduction. In this work, carbon quantum dot (CQD) decoration and oxygen atom doping were applied to CN by a facile one-step hydrothermal method. The incorporated CQDs not only facilitate charge transfer and separation, but also provide alternative CO₂ adsorption and activation sites. Further, the oxygen-atom-doped CN (OCN), in which oxygen doping is accompanied by the formation of nitrogen defects, proves to be a sustainable H⁺ provider by facilitating the water dissociation and oxidation half-reactions. Because of the synergistic effect of the hybridized binary CQDs/OCN addressing the three challenging issues of the CN based materials, the performance of CO₂ photocatalytic conversion to CH₄ over CQDs/OCN-x (x represents the volume ratio of laboratory-used H₂O₂ (30 wt.%) in the mixed solution) is dramatically improved by 11 times at least. The hybrid photocatalyst design and mechanism proposed in this work could inspire more rational design and fabrication of effective photocatalysts for CO₂ photocatalytic conversion with a high CH₄ selectivity.