Magnetic cobalt ferrite (CoFe2O4) was extensively investigated for the activation of peroxymonosulfate (PMS) to generate sulfate radicals. In this study, the CoFe2O4 nanoparticles were uniformly decorated on graphene oxide (GO) nanosheet. According to the large surface area and more surface oxygen species, the CoFe2O4-GO composite exhibited much better efficiency than CoFe2O4 for the generation of sulfate radicals. The degradation of antibiotic norfloxacin (NOR) by CoFe2O4-GO coupled with PMS was comprehensively investigated. Through radical quenching study and electron paramagnetic resonance (EPR) analysis, the active radical species were elucidated. The underlying mechanism was then discussed based on the detected radicals and X-ray photoelectron spectroscopy (XPS) observations. It was revealed that the NOR degradation by CoFe2O4-GO system was dominated by a nonradical process rather than a radical process. The surface oxygen species at defective sites of GO played a critical role in the degradation process. Finally, the developed CoFe2O4-GO composite showed a good potential for the remediation of NOR polluted natural river/lake water.