Abstract: In the third-generation advanced nuclear station demonstration project (CAP series), specific areas and equipment have high technical requirements for supporting cables, and there is a lack of key insulating materials in China. The different phenyl silicone rubber matrixes from the perspective of high-temperature resistance and radiation resistance were slected, the influence of different heat-resistant agents, hydrophobic modified additives, and flame retardant systems on the heat resistance, humidity resistance and flame retardant properties of the silicone rubber composites were studred and thus this article developed novel halogen-free, flame-retardant, heat-resistant, radiation-resistant silicone rubber material which meets technical requirements. The electrical, physical, combustion, accelerated thermal aging and conventional radiation aging performance of specific cable for pressurizer immersion heater prepared with it as insulation meets the technical target of the project, which realizes independence and control of key component materials and core technology.