To enhance the radiation stability of silicone rubber (SR) and ensure its safe and reliable performance,hexagonal boron nitride (h-BN) was incorporated into SR as a functional filler. The effects of the filler amount and size on the mechanical properties,thermal stability,and radiation resistance of SR composites were investigated. The mechanism through which h-BN improved the radiation stability of SR was explored. The experimental results of stress-strain and hardness tests showed that the SR composite filled with 20 parts of h-BN (BN/SR-20) exhibited excellent mechanical properties. The tensile strength,100% constant tensile stress (S₁₀₀),and hardness of BN/SR-20 improved by 5.9%,69.1%,and 15.6%,respectively,compared with those of unfilled SR (SR-U). BN/SR-20 displayed higher radiation resistance than SR-U,and its tensile strength and S₁₀₀ were significantly better than those of SR-U in an ionizing-radiation environment. A larger transverse size of h-BN was found to be more effective in slowing down the radiation-aging process of SR. In addition,gas chromatography analysis of the radiolytic gas (hydrogen) yield and oxygen consumption of the composites and free-radical-scavenging experiments revealed that the addition of h-BN reduced the diffusion rate of O₂ in SR and enhanced the radiation resistance of the composites.