Abstract: Carbon fiber reinforced composites are widely used in ablative thermal protection systems (TPS). The microstructures of the composites are greatly related with the ablation behavior. Thus, the study of micro-ablation mechanisms of the composites is significant for the material design and manufacturing. A mathematic micro-ablation model is developed by using the finite-volume-method (FVM) combing with the piecewise linear interface calculation (PLIC) method. Comparing with the analytical results, the numerical method is validated by calculating the ablation morphologies for single fiber embedded in carbon matrix. The effect of carbon fiber inclination on the microscopic ablation behavior is studied for the unidirectional carbon reinforced composites with different carbon fiber inclination. The results are found that the ablation morphology for carbon fiber is bamboo shoot shape if the oxygen diffusion rate is far greater than that of carbon oxygen reaction when the oxidation resistance of carbon fibers is stronger than that of matrix. If the carbon oxygen reaction rate is far greater than that of oxygen diffusion, carbon fiber and matrix will be ablated at the same rate. When the oxidation resistance of carbon fiber is stronger than that of the matrix, the inclination angle of the carbon fiber has a great influence on the micro-ablation behavior of the material. On the contrary, the effect is not significant.