Abstract: Disclosed is a method of quantifying furan concentration to efficiently manage a deterioration state of a transformer in the field. The method of quantifying furan concentration includes: measuring a color-development degree of an extraction solution by making the extraction solution containing furan extracted from an insulating-oil sample mix and react with a color reagent; and quantifying furan concentration by correction based on a correlation between a precise analysis and a simple analysis with regard to the color-development degree of the extraction solution, wherein the precise analysis is to obtain a quantitative value through color column separation based on high performance liquid chromatography (HPLC) in a laboratory to analyze a furan compound in insulating oil of a transformer, and the simple analysis is to obtain a chromaticity value in a field with regard to actual transformer samples.