Aiming at the problems of expensiveness and pollution of physical and chemical demulsifiers in the process of oilfield sewage demulsification，it is advisable to study and synthesize green and environmental friendly demulsifiers. Glycolipid biosurfactant-producing T strain microorganism was cultured aerobically in the medium for 6 d， then the fermentation centrifugation supernatant was mixed with water to prepare centrifugation supernatants with different volume ratios. The supernatant was used as a solvent. A biosurfactant（BS）-stabilized nano iron sol was prepared by a combination of sol-gel and solvothermal methods. The nano iron sol stabilized by BS was characterized by scanning electron microscopy，X-ray diffraction，infrared spectroscopy，laser particle size analyzer and Zeta potentiometer. The factors affecting its morphology，size，phase，functional group，sol stability and particle size distribution were studied. The demulsification performance of the nano iron sol on the oily sewage emulsion prepared by the oil-water mixture on Weizhou Island was investigated. The results showed that when the volume fraction of supernatant was 80% and 100%，the iron particles with a particle size of about 200 nm and 40—200 nm could be synthesized，respectively. The Zeta potential electronegativity of the iron sol prepared with 20% supernatant was the strongest. The colloidal stability was the highest. When the volume fraction of supernatant was 60%，the nano iron sol product had the best demulsification effect. It could produce a good demulsification effect on the oil-in-water emulsion formed by sodium dodecyl sulfate at low temperature. After standing for 24 h，the dehydration rate reached 78%. The demulsification effect on the sewage at the Nanhai terminal site was obvious. It was recommended to combine biological metabolite with chemical agent and prepare environmental friendly composite nano demulsifier，meanwhile，study their reuse and other issues in the future.