Ternary heterojunction TiO₂/g-C₃N₄/Ag₃PO₄ photocatalyst，loading the calcinated TiO₂/g-C₃N₄ composite on the surface of Ag₃PO₄，was successfully prepared by in⁃situ precipitation for the degradation of Rhodamine B（RhB） dye.The composition，microstructure and physicochemical properties of the samples were characterized by X-ray diffraction（XRD），scanning electron microscopy（SEM），ultraviolet visible diffuse reflectance spectroscopy（UV-vis DRS）.The results showed that TiO₂ nanoparticles with the particle size of about 100 nm were uniformly supported on the surface of g-C₃N₄ and Ag₃PO₄ in TiO₂/g-C₃N₄/Ag₃PO₄ photocatalyst，and the absorption edge of the heterojunction underwent a red shift.Excellent photocatalytic activity of TiO₂/g-C₃N₄/Ag₃PO₄ under visible light irradiation was demonstrated by degrading RhB dye.After exposure to visible light for 7 min，the degradation rate of RhB by TiO₂/g-C₃N₄/Ag₃PO₄ photocatalyst could reach 99%，which was obviously higher than that of pure g-C₃N₄，TiO₂，Ag₃PO₄ and binary complex，and its photocatalytic degradation rate remained above 92% after repeated use for 5 times，indicating its strong photocatalytic activity and excellent stability.Moreover，the photocatalytic degradation mechanism was explored through the capture experiments.In this ternary heterojunction，g-C₃N₄ with π-conjugate structure facilitated charge transfer.Under the irradiation of visible light，the photogenerated electrons accumulated in the conduction band of g-C₃N₄，and the photogenerated holes accumulated in the valence band of Ag₃PO₄ and TiO₂，thus e^--h⁺ pairs were separated effectively to improve the separation efficiency of photogenerated carriers.The primary active species of photocatalyst were photogenerated holes（h⁺） and superoxide free radicals（·O₂^-），while e^- basically had no effect.