As typical persistent organic pollutants, polybrominated diphenyl ethers (PBDEs) have aroused high environmental concern due to their toxicity and recalcitrant degradation. Herein, we report the enhanced photoreduction degradation of polybromodiphenyl ethers with Fe₃O₄-g-C₃N₄ under visible light irradiation (>420 nm). A series of high activity photocatalysts Fe₃O₄-g-C₃N₄ (named FeOCN-x) have been synthesized by an in situ growth method. The characterization of the prepared FeOCN-x nanocomposites has been examined by SEM, TEM, ultraviolet-visible diffuse reflectance spectroscopy, a vibrating sample magnetometer, X-ray diffraction, X-ray photoelectron spectroscopy and Brunauer–Emmer–Teller surface area analysis. FeOCN-x hybrids all exhibit good magnetic separation properties with the saturation magnetization at 300 K varying from 0.4 to 6.3 emu g⁻¹. Under visible light irradiation, FeOCN-x hybrids show enhanced photocatalytic activity for the debromination of PBDEs compared with g-C₃N₄. Among all the hybrids, FeOCN-4 with a 4 wt% Fe₃O₄ content gives the highest reaction rate, which is 6.7 times as high as that in pure g-C₃N_4. The FeOCN-x nanocomposites not only exhibit good photostability, but could also be easily recovered by magnetism. The results of the kinetic isotope effects (KIE) and the trapping agent experiments show that the rate determining step in the degradation reaction of PBDEs with FeOCN-x is the rate of electron accumulation in the conductive band. A possible photoreductive mechanism has been proposed. This study shows that the easily magnetically separable recycled photocatalyst FeOCN-x, with high visible light activity, could be an excellent candidate for dealing with halogen pollutants.