g/C3N4-ZnO composite catalysts were synthesized through surface hybridization of the delocalized conjugated-π structure of g/C3N4 with the closely contacted surface of ZnO via a successive and simultaneous calcination procedure, and two kinds of photocatalysts, g/C3N4-ZnO1 and g/C3N4-ZnO2, were obtained. Heterojunctions were formed between the two components, which promote the separation of photogenerated carriers efficiently, and then enhanced the degradation of 100mg/L of AMX. The degradation rate of g/C3N4-ZnO1 was 1.54, 11.33, and 2.52-fold that of g/C3N4-ZnO2, g/C3N4, and ZnO, respectively, at a 3.5-h reaction period, with the dosage of 0.3 g/L, and solution pH at 7.0±0.2. The recycle and reuse ability was excellent and 90.5% of AMX mitigation was achieved in the fifth cycle. For g/C3N4-ZnO1, electrons migrated from the conduction band of g/C3N4 to that of ZnO via the heterojunction. ·OH and h+ were the main active species for AMX degradation, compared to ·O2 - dominated for g/C3N4. Twelve intermediate products were identified, and two degradation pathways were inferred for g/C3N4-ZnO1 and g/C3N4- ZnO2, respectively. Finally, transformation products without lactam rings were achieved, which lost most of the antibacterial potencies, and the ecotoxicity was also dramatically decreased as indicated by the ECOSAR program.