In response to the water pollution caused by the excessive use of antibiotics, the photocatalytic degradation performance, cyclic stability, and reaction mechanism of SnO2/ZnO/C3N4 ternary composite photocatalysts were systematically investigated using tetracycline as the target pollutant. Composite catalysts with varying SnO2 loading levels (3wt%~7 wt%) were prepared via a combination of hydrothermal and calcination methods. The photocatalytic activity was evaluated through degradation experiments, while stability was assessed via cyclic tests. Active species trapping experiments were employed to identify key reactive intermediates, and a pseudo-first-order kinetic model was applied to analyze degradation rates. The results indicate that the 5 wt%  SnO2/ZnO/C3N4 composite (labeled 5-SnZnCN) exhibits the highest photocatalytic activity, achieving a degradation rate of 92.04% for 10 ppm tetracycline within 25 minutes under visible light irradiation. The represents a 12-fold, 2.6-fold, 90-fold, and 6.6-fold improvement over pure C3N4, ZnO, SnO2 , and binary ZnO/C3N4, respectively. The reaction kinetic rate constant of 5-SnZnCN was determined to be 0.079 77 min-1, significantly higher than that of other tested samples. Cyclic tests demonstrated that 5-SnZnCN maintains a degradation efficiency of 86.16% after four reuse cycles, highlighting its excellent stability. Trapping experiments confirmed that superoxide radicals (·O2-) are the primary active species in the photocatalytic degradation process. A high-performance photocatalyst and theoretical foundation for the efficient treatment of antibiotic-containing wastewater was provided.