Abstract: The dielectric frequency response method was used to model an oil-paper insulation system. The time domain dielectric response function and its frequency response were derived. An experimental system was designed to measure the dielectric frequency responses of oil-paper insulation at different temperatures. Also, the dielectric frequency response of the pure impregnated paper was calculated. The results show that the errors caused by the oil gap were not significant, with the maximum error being less than 10%. Significant dielectric loss of oil-paper insulation occurred in low frequencies, but not in high frequency. As the temperature increases, the shapes of oil-paper dielectric frequency response curves almost keep the same, and move to high frequency direction. The logarithm of dielectric loss of oil-paper is linear to reciprocal of temperature when frequency is constant.