Nowadays, the widespread concern over controlling CO2 emissions and mitigating the adverse effects of greenhouse gases on global climate has attracted significant attention. In this study, g-C3N4 was synthesized by thermopolymerizing urea. Subsequently, ZIF-8 was combined with g-C3N4 using an in situ deposition method, resulting in the fabrication of ZIF-8/g-C3N4 composite photocatalysts at various molar ratios. Effective incorporation of ZIF-8 into g-C3N4 suppressed the recombination of photogenerated electrons and holes, thereby enhancing CO2 capture capacity and preserving light absorption capabilities. The ZIF-8/g-C3N4 composite demonstrates excellent photocatalytic performance for CO2 reduction, where the optimized material exhibited a CO2 adsorption capacity 1.52 times that of pure g-C3N4 and increased the conversion of CO2 to CH4 by more than sevenfold. This study harnesses the superior CO2 adsorption properties of metal-organic frameworks to develop more efficient photocatalysts, enhancing CO2 conversion efficacy and offering insights for developing efficient photocatalysts that utilize CO2.