The —CH₃ atoms methane gas was filled to study the preparation and performance of the hydrogen-containing DLC( a-C:H) thin film. At different CH₄ / Ar flow ratio condition, the a-C:H was deposited on the N type silicon substrate. By means of ellipsometer, the non-contact white light interferometer as well as the laser wave interferometer, the deposition rate and surface roughness were lucubrated. Experiment results show that the deposition rate of the diamond-like carbon thin film is enhanced by the addition of the hydrogen-containing carbon gas and the surface flatness is also improved.