Abstract: A homogeneous and heterogeneous reaction mathematical model of multi-field coupling was developed according to the characteristics of thermal gradient chemical vapor infiltration (CVI) fabricating C/C composites, using 2D carbon felt as the preform, natural gas as the carbon source gas, the furnace pressure of 100 kPa. The time evolution of the preform density was obtained by calculation, the effects of deposition temperatures and gas flow rates on the densification process were analyzed, and the reasonable range of deposition temperature and gas flow rate were obtained. After the preform being infiltrated for 100 h, the overall and radial-direction densities of the preform from simulation agree well with those from experiment. The model is validated to reliable and the simulation has capability of forecasting the process.