Abstract: DC cables operate under high temperature gradients for a long time and are often subjected to transient voltages such as polarity reversal and impulse voltage, et al., which seriously threatens the reliability of cable insulation. In this paper, silicone rubber, the main insulation material for cable accessories was selected, and electrical tree initiation characteristics with varied temperature gradient under polarity reversal voltage were studied. A bipolar carrier transport model under extremely inhomogeneous fields was built, and the charge transportation and electric field distribution characteristics during different temperature gradients and polarity reversal voltages were studied. Results show that as the temperature of needle tip rises, the amount of space charge injection and the depth of injection continue to increase and the electric field changes more after the reversal. When the temperature increases from 30℃ to 120℃, the tree initiation voltage decreases by 26.2%, and the tree morphology tends to be dense, but the tree length first increases and then decreases. Combined with the characteristics of space charge transportation, the initiation process of electrical tree under polarity reversal was given, and the influence of temperature gradient on tree initiation characteristics was analyzed.