Abstract: In this paper, according to the analysis of the thermo-chemical mechanism, the change rules of ablation properties of the C/C composites in thermo-chemical ablation, ablation surface receding and temperature field coupling were investigated by finite element method. The receding of the ablation boundary by virtual failure and rebuilding orphan mesh part was achieved, and finite element model of ablation temperature field at receding boundary conditions was established.The net heat flux flowed into the material and ablation rate were calculated by the thermo-chemical ablation theory.The phenomenon of large local heat flux on the irregular surface was corrected by programming after ablation surface receding when the heat flux was reloaded.The result shows that as the ablation time increases, the heat flux flows into composite materials will reach a dynamic balance.The ablation of the material is the results of a variety of factors and coupled calculation can truly reflect the characteristics of the ablation of the material.