Abstract: Xanthate in mineral processing wastewater can do serious harm to environment. Bismuth vanadate can degrade xanthate under visible light, but its serious electron-hole complex affects its practicability, in view of the abundant pore structure and composition of coal gangue, the coal gangue supported photocatalyst (CG/BiVO₄) was synthesized by hydrothermal method. The catalysts were characterized by XRD, FTIR, SEM, UV-Vis DRS, PL, the photocatalytic degradation of xanthate and the mechanism of coal gangue modified bismuth vanadate were investigated under visible light. The results showed that the photocatalytic activity of the supported CG/BiVO₄ is significantly higher than that of the pure BiVO₄. Under the conditions of 20wt% coal gangue loading, pH=7, catalyst dosage is 1.5 g/L, initial concentration of xanthate C₀=10 mg/L, the degradation rate of xanthate over CG/BiVO₄ reached the maximum at 540 min, which was 93% . The photodegradation process of xanthate complied with the first-order kinetic model. After treatment, the concentration of chemical oxygen demand C_COD was 11.47 mg/L, which met the emission standard. The predicted degradation rate of 20%-CG/BiVO₄ was only 0.96% different from the actual degradation rate, which indicated that the model could predict the degradation rate of 20%-CG/BiVO₄. The results show that the loading of CG can significantly increase the specific surface area of the catalyst, improve its response to visible light, increase the separation efficiency of electrons and holes in the photocatalytic system, and decrease the recombination probability of photogenerated electrons and holes, this is an important reason for the improvement of the performance of the composite photocatalyst, the mechanism analysis showed that h⁺ was the main free radical in xanthate photodegradation, while •O₂ ⁻ and •OH were secondary, under the action of free radical, the alkyl group and C=S in the xanthate were firstly broken, and formed the intermediate product, peroxy xanthate (ROCSSO⁻) , then mineralized to form small molecules such as SO₄²⁻. After 7 h of photoreaction, the conversion of Sulfur was close to the degradation rate of xanthate, and the degradation rate was not less than 90% after 5 cycles, it can be seen that the catalyst has good photocatalytic performance, which lays a theoretical foundation for the resource utilization of coal gangue in the photocatalytic field.