The mathematical modeling for the preparation of C/C composites from propane by F-CVI (Forced-flow chemical vapor infiltration) was studied. Experimental data were fitted with the modeling calculations and an adjusted reaction rate constant was obtained. Effects of many operation parameters such as temperature, the inlet concentration of propane, flow rate, and the initial porosity were observed. The decrease of the deposition rate due to the decrease of porosity and the depletion of propane in the middle of the preform was compensated with the increase of the lateral surface area of fibers. It was confirmed that a slow reaction rate with a low temperature and a low concentration is necessary for a uniform infiltration. As the gas flow rate and the initial porosity increase, the amount of deposition increases.