In this paper, snowflake ferric oxide (α-Fe2O3) nanomaterials were prepared by one-step hydrothermal synthesis, and silver nanoparticles (AgNPs) were in-situ grown on the surface of the nanomaterials by chemical reduction method. AgNPs was used as surface enhanced Raman scattering substrate to detect furfural concentration in soybean based natural ester oil. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD), electrochemical workstation and Raman spectrometer were used for the characterization. The results showed that the lowest detection limit of RhB was 10-11 mol/L (M), and α-Fe2O3-AgNPs had better SERS performance than a single AgNPs substrate. The α-Fe2O3-AgNPs substrate was functionalized to modify 4-ATP molecules, and was used to detect furfural in soya-based natural ester insulating oil with the lowest detection limit of 0.05 mg/L. The test results fully meet the aging standards of insulation oil in the power industry (severe aging, 4 mg/L; moderate aging, 0.5 mg/L; mild aging, 0.1 mg/L).