Silicone rubber has high resistivity and remains stable over a wide range of temperatures and frequencies, with outstanding corona and arc resistance. This characteristic makes it an ideal insulating material for high-voltage cable accessories and widely used in cable accessories. However, the uneven distribution of electric field in the actual operation of the cable is particularly prominent, which is a key factor in reducing the insulating properties of silicone rubber. In this paper, SiR is endowed with nonlinear conductive properties by doping multi-walled carbon nanotubes (MWCNTs) with silicone rubber as the substrate. At the same time, an appropriate amount of boron nitride (BN) is doped to ensure its insulating properties. These two inorganic fillers were blended, and the MWCNTs/BN/SiR composite media with different mass fractions were prepared by regulating the doping content of the inorganic fillers, and the composite media were tested for microstructural characterization, variable-temperature conductivity, breakdown field strength and mechanical properties. The results show that the conductivity of the doped MWCNTs/BN filler composite media exhibits obvious nonlinear characteristics, while maintaining good breakdown strength and mechanical properties.