Silicone rubber (SiR) is widely used as the main insulating material in cable accessories and faces high temperature challenges during operation. Pulse overvoltages can threaten working state of the insulation. In order to understand electrical tree degradation process at high temperature under repeated pulse voltages, stress testing was performed in this experiment. The ambient temperature (Tamb) was set to 30, 60, 90, 120, and 150 ° C, and the frequencies of the pulses were set to 5, 20, 100, 200, and 1000 Hz, respectively. During operation, it is also threatened by mechanical stress, which is caused by the spring-clamping device and the expanded bundling force of the rubber stress cone, which will affect the electrical properties of the silicone rubber in the cable accessory. In this chapter, the growth characteristics of trees under tensile stress and compressive stress were studied by using the needle plane electrode system.