In order to develop an efficient adsorbent suitable for water body remediation，magnetic nanoparticles （Fe₃O₄ NPs） were prepared by green synthesis method using low-cost and easily-obtained Inonotus oblquus extract，and applied to the oil removal treatment of oily wastewater. This study aimed to cope with the challenges of high cost，complex process and low bioavailability in the preparation of traditional nanomaterials. The synthesized magnetic nanoparticles Fe₃O₄ NPs were systematically analyzed by Fourier transform infrared spectroscopy （FT-IR），scanning electron microscopy （SEM），transmission electron microscopy （TEM） and other characterization methods. The results showed that the bioactive substances in inonotus obliquus extract participated in the synthesis of Fe₃O₄ NPs as both reducing agent and stabilizer. The prepared Fe₃O₄ NPs were irregularly spherical，with an average particle size of 16 . 69 nm，a Zeta potential of - 31 . 7 mV，exhibiting good stability. The saturation magnetization of Fe₃O₄ NPs was 30 . 2 A · m²/kg. The magnetization curve showed that the material had superparamagnetism and was easy to be separated and recovered. The optimum conditions for oil removal by Fe₃O₄ NPs were as follows：concentration 500 mg/L，temperature 50 ℃，treatment time 30 min and stirring speed 200 r/min. The oil removal rate reached 90 . 24 %，demonstrating excellent oil removal performance. This study ingeniously integrates the advantages of nanotechnology，biotechnology，and green chemistry，providing a new approach for the green treatment of oily wastewater.