The cobalt nanoparticles decorated biomass Juncus derived carbon (Co@JDC) was prepared by facile calcination strategy and applied to activate peroxymonosulfate (PMS) for eliminating ofloxacin (OFX) in the water environment. The results of catalytic experiments show that 97% of OFX degradation efficiency and 70.4% of chemical oxygen demand removal rate are obtained within 24 min at 0.1 g L-1 Co@JDC, 0.2 g L-1 PMS, 20 mg L-1 OFX (100 mL), and pH = 7, which indicates that Co@JDC/PMS system exhibits excellent performance. Meanwhile, the experimental results of affect factor show that Co@JDC/PMS system can operate in a wider pH range (3-9) and Cl-1, NO3-1, and SO42- have an ignorable effect on OFX degradation. The radical identification experiments confirm that SO4˙-, ·OH, O2˙-, and 1O2 are involved in the process of PMS activation, especially SO4˙- and 1O2 are the main contributors. Furthermore, a possible PMS activation mechanism by Co@JDC was proposed and the degradation pathways of OFX were deduced. Finally, the stable catalytic activity, negligible leaching of Co2+, and the outstanding degradation efficiency for other antibiotics prove that Co@JDC possesses good stability and universality.