The invention discloses a method for quantitatively evaluating a moisture insulating degree of oil paper, which is based on a variable voltage inter-frequency dielectric loss curve. The existing powerfrequency dielectric loss test can only reflect a dielectric loss situation of equipment under a certain voltage of power frequency. The method disclosed by the invention comprises the steps of: performing voltage boosting test and voltage reducing test at a frequency different from but near the power frequency on the oil paper insulating equipment, and obtaining a variable voltage inter-frequency dielectric loss curve; after characteristics of the curve are met, extracting the characteristics of the variable voltage inter-frequency dielectric loss curve; performing comparison and analysis based on a numerical model library, and quantitatively analyzing the moisture content in the oil paper insulating equipment; and quantitatively judging the insulating situation of the oil paper insulating equipment. According to the method for quantitatively evaluating a moisture insulating degree of oil paper, the effective area between the voltage boosting curve and voltage reducing curve in the inter-frequency dielectric loss curves and the moisture content of the equipment are quantitatively correlated, thereby greatly simplifying the operation of the moisture content detection of the equipment and greatly improving the accuracy of the detection.