Abstract: Carbon aerogel composites exhibit excellent high-temperature stability, but their relatively high thermal conductivity limits their applications in high-temperature insulation. In this study, a novel approach for high-temperature-usable carbon aerogel composites (CAC) is proposed based on the low-temperature carbonization strategy. CAC with low density of ~0.4 g·cm⁻³ are prepared by polyacrylonitrile pre-oxidized fiber reinforced sol-gel polymerization of phenolic resin, followed by ambient pressure drying, and low-temperature co-carbonization. This preparation strategy effectively reduces the thermal conductivity of the material while ensuring its high-temperature stability, providing a new solution for the preparation and application of carbon aerogel composites. The graphitization degree and the thermal conductivity of CAC are strongly dependent on the carbonization temperature, in which the room temperature thermal conductivity increases significantly from 0.07 W·(m·K)⁻¹ to 0.15 W·(m·K)⁻¹with the increase of carbonization temperature from 600℃ to 900℃. Typically, the CAC prepared at a carbonization temperature of 700℃ exhibits a relatively low thermal conductivity of 0.085 W·(m·K)⁻¹ at room temperature. It also has excellent high temperature stability, mechanical properties, anti-ablation and thermal insulation properties at 1600℃, allowing it usable for high temperature insulation. In addition, the intrinsic thermal conductivities of the material at different carbonization temperatures are calculated using a reverse lattice Boltzmann method and the effective thermal conductivities are further predicted, which should provide the useful guidance for their thermal insulation performance.