Abstract: In order to analyze the deposition mechanism of carbon source during the chemical vapor infiltration process, using carbon fiber neddled flet as preform, propylene (C₃H₆) added natural gas mixture gas as carbon source, the effects of carbon source composition on densification of C/C composites and microstructure of pyrolytic carbon were investigated. The results show that compared with using natural gas as carbon source, using a moderate ratio of C₃H₆ added natural gas as carbon source can improve the densification efficiency and density distribution uniformity of C/C composites effectively. At the same time, it is beneficial to form high texture pyrolytic carbon. After deposition for 100 h under the optimal condition (9vol% C₃H₆), the density and density deviation at radial direction of C/C composites are 1.40 g/cm³ and 0.04 g/cm³ respectively, the pyrolytic carbon is homogeneous rough laminar structure, and the graphitization degree is high. While when using natural gas as carbon source, the density and density deviation at radial direction are 1.17 g/cm³ and 0.07 g/cm³ respectively, the pyrolytic carbon is binary banded structure, and the graphitization degree is lower. When the ratio of C₃H₆ is improved to 17vol%, the density and density deviation at radial direction of it are 1.28 g/cm³ and 0.10 g/cm³ respectively. Compared to the composite prepared under the optimal condition, the density and density distribution uniformity decrease obviously.