In order to meet the needs of online evaluation of the electrical insulating materials’ deterioration degree and remaining life under the pulse electrical stress, such as PWM regulating speed, the leakage current and its change law of the insulating materials under different deterioration degrees are researched. At first, the average life and lowest life of insulating film samples under the condition of corresponding accelerated stresses are determined through the accelerated aging experiments by using the pulse electrical stress accelerated aging experimental device. Then, a batch of preaging samples are created based on the aging model and the deterioration speed of the preaging samples is delayed by decreasing the pulse amplitude and keeping the frequency of accelerated factors invariant. The results of experiment show that the deviation degree between leakage current’s centroid and initial leakage current, the dispersion of leakage current and centroid of observation interval and the slope of leakage current are all related with the deterioration in the observation interval. The insulating deterioration which is defined by these three parameters can well describe the deterioration degree of insulating property.