Abstract: Study on the relationship between microphysical processes of electrical tree and macro characterization of PD in silicone rubber, can provide a theoretical basis of cable joints’ insulation condition online assessment based on PD severity. In this paper, the silicone rubber test sample with defect was made; and the electrical tree photos and PD signals were observed and measured during the deterioration process of the test sample; the time curves of electrical tree area and PD energy per unit time were obtained; the relationship between the two curves was expounded. Based on the change of electrical tree area, the development process of electrical tree was divided into three stages: growth, slow growth and rapid growth. The growth pattern of the electrical tree in every stage was discussed. The development of PD was divided into five stages according to the trend of PD energy. For each stage, the phase characteristic spectrograms were got; the cavity in PD gray images, and PD phase width were extracted to evaluate the severity of PD. The results show that, there was a highly consistency between the electrical tree curve and the PD curve. The three growth stages of electrical tree corresponded to the stage 1-2, stage 3 and stage 4-5 of PD development respectively. Thus, the relationship between electrical tree growth and PD development has been established, which laid the foundation for online assessment of the cable joint insulation condition..