Abstract: A 2D numerical model was established for simulating the chemical vapor deposition (CVD) of carbon in a vertical reactor. A full multi-component diffusion model was proposed to describe the diffusion of the gas species. The effects of Ar, N₂ or H₂ carrier gases on the flow field, species concentration and deposition rate of pyrocarbon were investigated using C₃H₆ as the carbon source. Results show that H₂ improves the stability of the gas flow. The concentration distributions of CH₄, C₂H₂, C₂H₄ and C₆H₆ are uniform in H₂. The pyrocarbon deposition rate is lowered, but the uniformity of deposition is improved when H₂ is used as the carrier gas compared with N₂ or Ar. The simulation results agree well with the experimental ones.