In order to develop efficient adsorbents for water body remediation, this paper green-synthesized magnetic nanoparticles Fe3O4 NPs using the low-cost and readily available birch bark extract, and applied them to the oil removal treatment of oily wastewater. The aim of this study is to overcome the challenges of high cost, complex process, and low biodegradability in the preparation of traditional nanomaterials. The synthesized magnetic nanoparticles Fe3O4 NPs were characterized by various methods such as infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that the bioactive substances in the birch bark extract acted as reducing agents and stabilizers in the synthesis of Fe3O4 NPs. The prepared Fe3O4 NPs were irregularly spherical in shape, with an average particle size of 16.69 nm. Their Zeta potential was -31.7 mV, indicating good stability. The saturation magnetization of Fe3O4 NPs was 30.2 Am2/kg, and the magnetization curve indicated that the material had superparamagneticsm, making it easy to separate and recover. The optimal conditions for oil removal by the synthesized Fe3O4 NPs were: concentration 500 mg/L, temperature 50℃, treatment time 30 min, and stirring speed 200 r/min. The oil removal rate was 90.24%, demonstrating excellent oil removal performance. This indicates that Fe3O4 NPs are a good oil removal material. This study ingeniously integrates the advantages of nanotechnology, biotechnology, and green chemistry, providing a new approach for the green treatment of oily wastewater.