Abstract: TCVI (Thermal Gradient CVI) process is a very potential process for C/C composite, by which C/C products with well distributed density can be manufactured in relatively shorter time. In this paper, the dynamic model and geometrical model of the process were established on the basis of theory of heat and mass transfer and structure character of the preform. According to these models, the technology of numerical simulation is applied to simulate and analyze the process. It's indicated by simulation that the preform is densified from interior to exterior during TCVI process so the external pores in the preform will not be sealed too early. The density homogeneity and the speed of deposition can be greatly improved by properly altering the thermal gradient in the preform. The result of simulation can lay the theoretical foundation for the development and application of TCVI process.