In order to improve the stress and the thermal stability of diamond like carbon (DLC) film, by adding two bubblers connected to mass flow controller into the improvement of the radio frequence plasma enhanced chemical vapor deposition (RF-PECVD) equipment, the DLC films with Si doping prepared by Rf-PECVD technology with CH4 as the reactants, liquid tetra methyl silane (TMS) as the reaction precurs and Ar as the carrier gas. The measurements of the stress, the hardness, roughness and the thermal stability demonstrate that the stress, roughness and the thermal stability of the DLC films doped Si are improved at a certain degree with the increase of the flow rate of the carrier gas, but the hardness decreases obviously, as the flow rate of the carrier gas is equal to 30 mL/min (standard state), the stress decreases to 0.65 GPa and the temperature of graphitization increases to more than 600 ℃, the roughness of the surface is decreased to 0.566 nm, but the hardness decreases to 12.6 GPa.