Abstract: Carbon/phenolic composite had been widely used as thermal protection system (TPS). Thus, in order to predict the ablation behavior of the carbon/phenolic composite, a mathematical model was proposed in this paper, which was based on the energy-and mass-conservation principles as well as on the thermal decomposition equation. The ablation process was simulated from the perspective of the fiber and matrix components. The thermal properties during ablation were calculated, and a moving boundary was implemented to consider the recession of the ablation surface. The temperature distribution, density, thermal properties, linear ablation rate and mass loss of the carbon/phenolic composite were predicted. The results show that the ablation of the carbon/phenolic composite is a highly nonlinear process of interaction of various factors. During ablation, the composite material has an uneven temperature distribution and the attenuation of the density on the ablative surface is the largest. In addition, the mass loss and mass loss rate almost increase linearly. The ablation behavior of the fiber and matrix is obviously different. Therefore, in order to provide more accurate reference and basis for the design of thermal protection materials, it is necessary to predict their ablation behavior respectively.