Abstract: According to the analysis of the volume ablative mechanism of thermal protective materials under elevated temperatures, the ablation-phase transformation properties and the thermomechanical behavior of the materials are investigated by Eshelby equivalent inclusion method. The interaction among different phases by thermal chemical reaction is considered using the hypothesis of the statistical uniform distribution for the pyrolytic phases (in the vacuum environment) in the materials. The elastic moduli of different matrix materials under different temperatures and heating rates are predicted. The results are in good agreement with experimental data.