The thermal response simulation model and method of ablation thermal protection system were studied.Charred layer-pyrolysis surface-original material layer model was applied to establish physical and mathematical model of thermal response and the axis-symmetrical thermal response of thermal protection system of spacecraft was computed by finite element method.The calculational formulas of pyrolysis gas mass flux and mechanism of heat transfer during ablation course were studied and analyzed deeply.Convection heat transfer between pyrolysis gas and charred layer was treated as heat source and it could speed up convergence of temperature field calculation by keeping the conductance matrix and capacitance matrix positive definite symmetric.The calculation results demonstrate that the mass flow of prolysis gas in the direction of thickness is over 80%,and side direction part is very small. The ablation scale is approximately 10mm, so the carton-carton material with good anti-ablation performance must be used in the tip of target;the ablation scale of body is less than 2mm,so the carton-phenolic aldehyde of small density can be used in thermal protection system of body.