Abstract: Silicone rubber of composite insulator is gradually aging and cracking under the action of complex factors such as heat and electricity in long-term operation, which will cause insulation breakdown failure in serious cases. In order to explore the influence of nano-SiO₂ on the thermal cracking process of silicone rubber composites at high temperatures, a nano-SiO₂/silicone rubber composite model was constructed by molecular simulation software, and the thermal cracking process of nano-SiO₂/silicone rubber composites was simulated by a reaction kinetics method. The research reveals that nano-SiO₂/MVQ composite system has a similar characteristic of MVQ in high temperature cracking and products, and molecular chains break at high temperatures, resulting in chain siloxane, accompanied by numerous molecular substances; nano-SiO₂ can inhibit the pyrolysis process of MVQ, and the inhibition gradually weakens with the increase in temperature. CH₄, C₂H₂ and H₂ are the main small molecular products of nano-SiO₂/MVQ system pyrolysis at high temperatures, and the amount of H₂ is far greater than that of other products. The breakdown failure of nano-SiO₂/MVQ composite insulation materials may be closely related to H₂. However, compared with MVQ, the nano-SiO₂/MVQ composite system has few products formation rate, quantity and cracking fragments, and the content and type of small molecules after thermal cracking are expected to be used as a reference standard for evaluating the thermal aging degree of composite insulator silicone rubber.