Broad application of nuclear energy has resulted in the release of radionuclides such as uranium [U(VI)], into the environment, and its potential toxic and irreversible effects on the environment are among the paramount issues in nuclear energy use. Graphite carbon nitride (g-C₃N₄) is a kind of non-metallic material with the triazine structure. In recent years, the reduction of U(VI) to insoluble U(IV) by g-C₃N₄ photocatalysis has become a major research focus on the area of radioactive pollutants. In this work, a metal-organic framework (MOF) material containing cobalt metal was used as a self-sacrificial template. Through simple thermal copolymerization, the Co-N_x coordination was successfully incorporated into g-C₃N₄ to synthesize the CoN_x/g-C₃N₄ photocatalyst. The effects of the morphology, structure, and photoelectric properties of CoN_x/g-C₃N₄ on the photocatalytic reduction of U(VI) were investigated using macroscopic batch experiments. The results showed that the introduction of Co effectively broadened the absorption range of g-C₃N₄ to visible light, inhibited recombination of the photogenerated electrons and holes, and facilitated the reduction of U(VI). Under irradiation in visible light for 45 min, pH 5.0 and solid-liquid ratio of 1.0 g/L, the photocatalytic reduction of a standard 50 mg/L U(VI) solution reached 100% by CoN_x/g-C₃N₄(w(Co-MOFs) : w(g-C₃N₄)=1 : 1). Furthermore, the photocatalytic mechanism of CoN_x/g-C₃N₄ was investigated through capture experiments. In summary, the CoN_x/g-C₃N₄ composite exhibits excellent optical performance, has simple operation, is eco-friendly, and has a significant photocatalytic effect on U(VI) in radioactive wastewater. This work also provides design strategy and technical reference for applying g-C₃N₄ materials to treat radioactive wastewater.