Carbon nanofibers with hollow structures have an excellent application prospect in various fields because of their high specific surface area and abundant active sites. PAN-based hollow carbon nanofiber doped with Co/CoO (H–Co/CoO–CNF) was successfully prepared and used as a catalyst to activate peroxymonosulfate (PMS) and degrade Rhodamine B (RhB). The catalyst showed a surprising degradation rate (98.89%) of RhB within 15 min and had good degradation performance in a wide pH range (pH 1.5–11.2). Compared with solid fibers, H–Co/CoO–CNF shows better cyclic characteristics. The catalyst is also magnetic and recoverable easily due to the addition of Co/CoO. Two pathways of both radical (SO₄^•−) and non-radical (¹O₂) exist during the RhB degradation process are confirmed through electron paramagnetic resonance (EPR) analysis and radical quenching experiments. This work provides a new idea for hollow fibers loaded with metals and their oxides and can guide the development of catalysts for advanced oxidation processes in the future.