Abstract: In order to further study the effect of Cr(VI) on the photodegradation of xanthate and its synergistic mechanism in the co-existing system of xanthate and Cr(VI), the photocatalyst of coal gangue/bismuth vanadate (CG/BiVO₄) was used, xanthate and Cr(VI) coexisting systems were studied by photocatalytic activity test, UV, FTIR, ion chromatography and quenching experiments, the photooxidation of xanthate and photoreduction of Cr(VI) and their synergistic mechanism were explored. The results show that there is a significant synergistic effect between the photo-oxidation of xanthate and photo-reduction of Cr(VI) in the co-existence system of xanthate and Cr(VI). Then, at the xanthate of 25 mg/L and the pH value of 7, with the dosage of catalyst being 1. 5 g/L, at the Cr(VI) of 2.0 mg/L, the removal rate of xanthate and Cr(VI) by CG/BiVO₄ are the best during a period of 480 min, reaching 98.81% and 88.80% respectively. The predicted degradation rate of xanthate is 94.79% by response surface methodology, lower 3.82% than the actual degradation rate, which indicates that the model can be used to predict the degradation of xanthate in the co-existing system. In the co-existing system, the vibration of C=S is changed first, followed by C—O—C, S—H, S—C—S, butyl, and the intermediate product peroxy xanthate (ROCSSO⁻) is formed after the visible light illumination 3 h , the highest conversion of sulfur is reached 97.94% after the visible light illumination 7 h. The synergistic mechanism analysis shows that the photogenerated e⁻ are rapidly captured in the photo-reduction of Cr(VI) and photogenerated h⁺ are consumed by xanthate photodegradation. The photogenic electron and hole pairs are consumed, on the one hand, due to the inhibition of photogenerated electrons and holes recombination, the lifetime of photogenerated electron and hole pairs are prolonged, on the other hand, the rapid consumption of photogenerated electron-hole pairs accelerates the conversion of light energy to chemical energy, generating a large number of photogenerated electron-hole pairs, therefor promoting the synergistic removal of xanthate and Cr(VI) .