Based on the design requirements of solid engine thermal protection system and external heat protection materials，the thermal stability and ablation properties of the two external heat protection materials were tested and analyzed by taking the self-made epoxy-based and silicone rubber-based external heat protection materials in use as the research object，and the specific heat capacity，thermal conductivity，thermal diffusion coefficient，average linear expansion coefficient and other thermophysical properties，so as to obtain the thermal stability and ablation properties of the two external heat protection materials.The results showed that the matrix structure of the epoxy-based external heat protection material after ablation was relatively loose，and the carbon layer formed by the silicone rubber base external heat protection material was more dense.The thermal conductivity of epoxy-based and silicone rubber-based external thermal protection materials within 250 ℃ changed little with the increase of temperature， and they were at a low level.The thermal conductivity of the external heat-resistant material after ablation gradually increases with the increase of temperature， and the average linear expansion coefficient gradually decreases.Compared with the two external heat protection materials， the introduction of high-temperature resistant fibers and flame retardants in silicone rubber-based external heat protection materials requires higher thermal decomposition activation energy，improves the ablation resistance and erosion resistance of external heat protection materials，and can meet the higher heat flow environment. The study of thermal and physical parameters and ablation mechanism before and after ablation of external heat-resistant materials can guide the development of external heat-proof materials.