Abstract: The heat and mass transfer in the ablation process are of great importance for the ablation protection engineering. In this work, the effect of permeability on heat and mass transfer and ablation thermal protection of gases produced during ablation were studied. Since the carbide formed by ablation of material is a typical porous medium, its structure has self-similarity and can be described by fractal theory. Taking account into the relationship of global coordinates and local coordinates, fractal permeability tensor was introduced into the ablation equation in this paper. In order to verify the correctness of this method, the simulation results were compared with the classical experiments. To simulate the ablation process, the temperature of three-dimensional spherical head with different pore area fractal dimensions and tortuosity fractal dimensions were simulated numerically. It is found that the higher the tortuosity fractal dimensions, and the lower the pore area fractal dimensions, the better the thermal protection.