Finite element method (FEM) was used for planar ablation problem of heat protection materials based on thermal analysis. ANSYS, a commercial FEM code, was employed for modeling and calculating, and material deleting and boundary moving problems were solved with its advanced techniques. Various heat flux (HF) densities ranging from 1 to 10 MW/m2 as thermal loads were investigated to the effects of heat conduction and ablation, respectively. The results showed that a sudden thermal load can cause great temperature rise and high thermal gradient near the surface of the material. The ablative quantity and ablation rate were also calculated, and mathematical models have been deduced for them.