Flexible silicone aerogels were prepared through sol-gel polymerization of methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS), followed by ambient pressure drying. The effects of mole ratio of MTMS to DMDMS on the chemical composition and microstructure of silicone aerogels were analyzed. Furthermore, flexible aerogel composites with a low density of around 0.25 g/cm³ were prepared by using mullite fiber blanket as structure reinforced agent. The as-prepared composites have excellent flexibility, good thermal stability and low room-temperature thermal conductivity below 0.03 W/(m·K). When the ratio of MTMS to DMDMS was optimized to 3.8∶1.2, the resultant composites had the highest tensile elongation of 3.6% and char yield of 82%. After calcination of the composites, the silicone aerogels were convent into inorganic SiO₂ aerogels with similar microstructure and thermal insulation. In static assessment of quartz lamp heating for 500 s, the surface of composites occurred ceramic reaction without obvious shrinkage at thickness direction, and there was 81℃-rise of their back temperature, demonstrating the combined functions of organic ablator and inorganic insulation properties.