The dielectric barrier discharge (DBD) can produce non-equilibrium plasma at about atmospheric pressure. The merits of deposition DLC films by vehicle of DBD plasma involve the simplicity of the experimental setup, the lower consumption of the feed gas and the electric energy, as well as the large-area deposition on various substrates at room temperature. From 1999, the research work has been developed in our laboratory. Films with high quality have been deposited. In the synthesis of DLC films by plasma enhanced chemical vapor deposition (PECVD), the dilution gas in the hydrocarbon will affect the properties of DLC films. However, this kind of research in DBD-PECVD is not reported. This work will research in the effect of Argon and Helium dilution into CH4 on the DLC films in the course of DBD-PECVD. The main contents of this work are as follows:The DLC films have been deposited by DBD-PECVD in He (or Ar)+CH4 at pressure of 60~150Pa. The effect of CH4 composition ratio on the properties of DLC films is examined. The hardness of DLC films increased with the decrease of CH4 composition ratio. At the same CH4 composition ratio- 33%, the nanohardness of the coating deposited in He+CH4 and Ar+CH4 reach the peaks - 20GPa and 18GPa. The RMS and the deposition rate of DLC films decreased with the CH4 composition ratio decreased. The FTIR absorption and Raman analysis of the coating confirms the results. The morphology and RMS of the films is examined by AFM. The thickness of DLC films is measured by SEM.The mechanism of the effects of He (or Ar) dilution on the properties of DLC films is discussed. The metastable state energy of He is 19. 8ev. This will lead to the enhancement of the energy and concentration of the electron, which will excite CH4 to CHn(n=l-3) and H atoms. The metastable state energy of Ar is 11.55ev. It can only enhance the concentration of the electron, which can also increase the concentration of H atoms. The increase of H atoms can lead to the increase of the film hardness and the decrease of the RMS of the films.