Abstract: Silicone rubber is widely used in the manufacture of insulators and other insulating components due to its excellent insulation, arc resistance, and heat resistance. In engineering, the method of installing silicone rubber insulation sheath is commonly used to improve the insulation level of electrical equipment, whereas, the thermal conductivity of ordinary silicone rubber material is only 0.27 W/(m·K), therefore, the heat dissipation of electrical equipment after installing insulation sheath has also become an urgent problem to be solved. Based on this, this paper establishes a three-dimensional model of the cable connector with the insulating sheath. Based on the finite element software, the influences of the thickness of the insulating sheath, thermal conductivity, working current and ambient temperature on its temperature transient changes are analyzed, and the three-dimensional axial temperature distribution of insulation sheath under thermal stability state is analyzed. The results show that, influenced by the temperature coefficient of the fittings, the rise of interface temperature of insulation sheath is non-linear with the increase of working current and ambient temperature. Thermal conductivity of insulating sheath material is the main factor affecting its temperature transient change and distribution. The higher the thermal conductivity is, the shorter the time for the sheath interface to reach thermal equilibrium will be, and the farther the heat will travel in the same direction.