In response to the serious problem of trace pollutants in the natural environment, photocatalytic degradation technology has become an effective solution for trace pollutant removal. Defective carbon nitride (g-C₃N_x ) materials have attracted much attention because of their superior visible light absorption properties. In this study, the Co₃O₄/ZnO@MG-C₃N_x visible photocatalyst was prepared by mixing the magnetic MG-C₃N_x material as the precursor CoZn-ZIF with different ratio of Co to Zn, and then calcinated at 900 ^oC. The structure, morphology and composition of the prepared photocatalyst were characterized by means of XRD, SEM, TEM, TGA and BET, to verify the successful preparation of the catalyst. It follows that the catalyst with the optimal ratio of Co∶Zn = 5∶1 possessed the excellent visible light catalytic activity, and the degradation rate of methylene blue (MB) reached 95.4% within 150 min. The catalytic efficiency of this catalyst was 4.77 and 2.2 times higher than that of G-C₃N₄ and Co₃O₄/ZnO, respectively. It was shown that the formation of a large number of nitrogen defects on the surface of G-C₃N_x after alkali activation was conducive to accelerating the capture of photogenerated electrons, and the promotion of synergistic interaction between the metal active sites led to an obvious acceleration of the photogenerated electron-hole separation and migration, which in turn enhanced the photocatalytic activity. The main active species were verified to be 1O₂ and ·OH by the active species capture experiments. In conclusion, the catalyst has excellent visible light absorption performance, stability and recyclability, and has a broad application prospect.