In this paper, we establish a thermochemical ablation model of C/C composite based on the lattice Boltzmann method, in which the flow, diffusion, chemical reaction, heat transfer, and the evolution of solid phase are comprehensively considered. In the model, the flow, mass transport and heat transfer, chemical reaction, and the evolution of solid phase are addressed by the multiple relaxation time model, the single relaxation time model, boundary condition, and the volume of pixel method, respectively. Then, we research the ablation process of carbon fibers based on the pore-scale using this model, and we discuss the effects of temperature field, inlet temperature, inlet velocity, and inlet concentration. Numerical results indicate that H2O contributes more ablation than CO2. Without temperature source term, increasing inlet temperature, inlet velocity, and inlet concentration can accelerate ablation. (C) 2018 Elsevier Ltd. All rights reserved.