Bushing fault is one of the prime reasons causing transformer faults, among which the failure rates caused by humidified insulation is in the first place, and correlative researches have verified that moisture is a key factor leading to paper oil insulation degradation, therefore, it is of great significance to research the influence of moisture on condenser bushing’s dielectric property. Oil-impregnated paper condenser core samples with different initial moisture contents are prepared, then an accelerated thermal aging laboratory test is carried out, and dielectric loss characteristics interval integral model is established. Results show that the integral values of ageing time and dielectric loss within the feature region comply with the linear rule, and the integral breadth of moisture and dielectric loss within feature region still comply with linear rule, which means that the integral value of dielectric loss can reflect the aging degree of insulation, the results of this paper provides a basis for further analysis on dielectric loss based oil-impregnated paper condenser bushing aging assessment and on insulation aging acceleration caused by moisture.