Ball-milled biochar with enhanced physicochemical and sorption properties has been intensively investigated, but its photochemistry property was far less studied. In this study, biochars from various pyrolysis temperatures were ball milled and tested for enrofloxacin (EFA) photocatalytic degradation and mechanisms. Ball-milled biochar could generate more •O₂^- under visible light irradiation, which favored the photocatalytic degradation of EFA. The ball-milled biochar pyrolyzed at 300 ℃ (BM300) exhibited the highest EFA degradation rate (66.3% compared to 13.9% for unmilled biochar). Characterization results suggested that the higher specific surface area and smaller particles size facilitated the adsorption of EFA molecules, while the abundant defects, more oxygen functional groups and persistent free radicals (PFRs) played significant role in the generation of reactive oxygen radicals (ROS), which benefited the enhancement of photocatalytic performance. Radical trapping experiments and electron paramagnetic resonance (EPR) technique confirmed that •O₂^- and h⁺ were the main active species in the photocatalytic degradation process. Based on the characterization and experiment results, a possible photocatalytic mechanism and degradation pathway of EFA by BM300 was proposed. This work promoted the BM biochar technology through improving current understanding of the fundamental processes and mechanisms that govern the photochemistry properties of BM-biochar. It provides new opportunities for the application of ball milling in environmental remediation.