The antibiotic levofloxacin was degraded by three steps of calcination, hydrothermal reaction and in situ precipitation using g-C₃N₄ as the substrate, and ZnO and Ag₃PO₄ were effectively combined to form a ternary photocatalyst of Ag₃PO₄/C₃N₄/ZnO. The morphology, structure and optical properties of the photocatalytic materials were investigated using XRD, FTIR, SEM, XPS and UV–Vis, and it was found that the three monomer materials, Ag₃PO₄, g-C₃N₄ and ZnO, formed Z-type heterojunctions, which increased the active sites of the photocatalytic materials and broadened the visible absorption spectra of the synthesized composites. The best degradation effect of Ag₃PO₄/C₃N₄/ZnO on 10-mg/L levofloxacin was achieved with the addition of 10% ZnO, the dosage of 0.5 g/L and the pH value of 5. The composites were characterized by the high efficiency of degradation of levofloxacin. The degradation rate of levofloxacin was maintained as high as 78.2% after 5 cycles of the experiment, which demonstrated the excellent recyclability of the photocatalytic material. Levofloxacin was decomposed by the Ag₃PO₄/C₃N₄/ZnO photocatalyst, and by analyzing the results of the electron spin resonance experiments and the capture test results, it was found that ·OH only played a small role, and h⁺ and O₂⁻ were the main oxidants. Based on the coupled liquid mass spectrometry analysis, the main steps in the degradation process of levofloxacin were the removal of methyl and carboxyl groups, the release of fluorine and the destruction of piperazine and quinoline rings.