The aging of high voltage oil-filled cable insulation is closely related with the generating and developing of the micro-defaults in the insulation and to the deteriorating of the oil/paper insulation. In this paper

the high voltage oil-filled cable insulating structure is investigated

and the infrared spectral analysis is used to analyze the cable oil samples in different thermal aging stages. The experimental results show that the quantity of furfural in cable oil can be measured by infrared spectral analysis; the aging of paper insulation tends to accelerate while the aging time prolonging; and the criticality of insulation aging can be reflected by the ratio of furfural to H2 content in cable oil （KFH）. The higher the saturated value of KFH is

the greater the danger to insulation remaining life of high voltage oil-filled cable is.