In order to illuminate the principle of thermal gradient chemical vapor infiltration (TCVI) technology for preparation of carbon/carbon composites, the change of resistance and power as a function of deposition re-gimes was measured and discussed in this paper. The results show that resistance values decrease non-linearly as a function of deposition regimes, and power values increase non-linearly as a function of deposition regimes. A high-textured carbon/carbon composites of Φ 240 mm ×Φ 80 mm × 33 mm was obtained in 320 hours. The fine bulk density(1.70 g/cm3) was measured. The microstructure of pyrocarbon, including the rough laminar, the smooth laminar pyrocarbon, have been observed and analyzed by polarized-light microscopy.