Abstract: In order to broaden the degradation temperature region and improve the ablation properties of spacecraft thermal protective coating, two kinds of typical silicone rubbers are investigated by TG-DTG analysis. Meanwhile, the static ablation properties and the thermal degradation mechanism of the rubbers filled with silica particles, mica, and red iron are studied respectively by the muffle roaster test. The thermal degradation mechanisms are characterized by SEM and FT-IR. Lastly, the ablation properties of the two kinds of silicone rubber- based coatings are tested by muffle roaster test and high temperature gas flow ablation experiment. The results show that for the methyl phenyl silicone rubber at the first thermal pyrolysis stage (220 ℃ to 320 ℃), the side group cross linking plays an important role; at the second thermal pyrolysis stage (320 ℃ to 480 ℃), the main chain’s “back biting” is the major reaction; at the third stage (480 ℃ to 630 ℃), the cyclic degradation occurs by the inter-chain folding. The main chain’s “back biting” weakens the resin's cross linking reaction and lead to mechanical degradation, producing “pulverization”. As for the methyl vinyl silicone rubber, the side group cross linking is essential during the degradation process, which promotes the resin’s cross linking reaction and thus improves the thermal stability. Compared with the other fillers, the silica particles can significantly improve the thermal stability of the two silicone rubbers, while mica and red iron also tend to slow down the thermal degradation rate.