A model for chemical vapor infiltration is applied to the study of the growth of alumina from the chemical reaction among AlCl3, H2, and CO2 within a SiC-fiber bundle which is situated in an isothermal hot-wall reactor. The pore space between the fibers is simulated by cylindrical capillary tubes. The model considers binary diffusion of CO2 and H2, chemical reaction on the inner surface of the tube, and deposition film growth. Furthermore, diffusion-controiled and chemical-reaction-controlled processes are taken into account to determine the dominating process in chemical vapor infiltration. Both molecular diffusion and Knudsen diffusion are considered sequentially in this model during the infiltration process. Based upon this model, the optimum processing conditions required for chemical vapor infiltration to form a SiC/Al2O3 composite can be predicted for different fiber preform systems.