Abstract: Electrical characteristics of coal mine high voltage cable was analyzed under situation of water tree aging, electrical tree aging and overall uniform deterioration. Wavelet noise canceling technology and signal separation technology based on orthogonal decomposition were used for noise signal processing of grounding line current. Changing trends and set threshold of grounding line current were used to determine whether cable insulation deterioration occurs. Matlab simulation results show that researching relationship between insulation parameters changing of each line and different components of corresponding grounding-line current enables extraction of characteristic signal of online monitoring of high voltage cable insulation degradation of coal mine.