Abstract: A ternary composite photocatalyst NH₂-UiO-66/BiOBr/Bi₂S₃ was successfully prepared by solvent thermal method. The crystal structure and microscopic morphology of the photocatalyst were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic activity and stability was investigated by catalytic degradation of colored dyes methylene blue (MB, 20 mg/L) and Rhodamine B (RhB, 20 mg/L) under visible light. The results show that UBB composite photocatalyst has the best photocatalytic performance when the content of NH₂-UiO-66 is 2%, and the degradation rate of MB (20 mg/L) and RhB (20 mg/L) could reach 93.5% in 60 minutes, 98.3% in 30 minutes, respectively. The photocatalytic degradation rate remains above 70% when the initial concentration of MB and RhB increas to 100 mg/L. After four cycles of experiments, the photocatalytic activity of UBB could not decrease significantly. Using ultraviolet-visible diffuse reflectance spectrum (UV-vis DRS), fluorescence spectroscopy (PL) and Electrochemical Impedance Spectroscopy (EIS), the reasons for the photocatalytic performance change of UBB were studied. Combining with Mott-Schottky (M-S) curves and active substance trapping experiments, a double Z-type electron transfer mechanism of this ternary system was proposed.