Abstract: According to the analysis of the thermal chemical ablative mechanism of resin matrix materials under pyrolytic reaction at elevated temperature, the ablation-phase transformation properties and the thermal deformation behavior of the materials were investigated by Eshelby equivalent inclusion method. The interaction among different phases by thermal chemical reaction was considered using the hypothesis of the statistical uniform distribution for the pyrolytic phases (in the vacuum environment) in the materials. The thermal expansion coefficients of different resin matrix materials under different temperature and heating rates were predicted. The results are in good agreement with experimental data.