Sillenite bismuth ferrite (S-BFO) was prepared by a co-precipitation-low temperature hydrothermal technique. The catalytic performance of S-BFO was evaluated by activating peroxymonosulfate (PMS) to remove ciprofloxacin (CIP). The results showed that adding 0.675 mmol/L PMS and 1000 mg/L of catalyst at the condition of initial pH value (6.5±0.1) and reaction temperature (25±1)℃, the removal rate of CIP (5.0 mg/L) was reached 84.8%. Under the same reaction conditions, the degradation efficiency of S-BFO activated PMS for CIP was higher than persulfate (PS). The morphology and crystal structure of S-BFO were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The effects of PMS concentration and initial pH value on the degradation of CIP in S-BFO/PMS system were investigated. The application potential of S-BFO/PMS system in the treatment of pollutants under real water conditions was evaluated. The results of ROS quenching experiments indicated that 1O2 is the main ROS in the S-BFO/PMS system, rather than $\cdot \mathrm{SO}_4^{-}$ or ·OH. The mechanism of degradation of CIP in the S-BFO/PMS system was also proposed. Finally, the 9 main products and intermediates of CIP were analyzed using liquid chromatography tandem mass spectrometry (LC/MS/MS) technology, and two possible degradation pathways was proposed including hydroxyl addition reaction (Pathway Ⅰ) and decarboxylation reaction (Pathway Ⅱ). This study provides important theoretical support for advanced oxidation technology based on persulfate in the field of wastewater treatment.