We studied deposition of low-k SiOCH dielectric film by PECVD. DEMS(diethoxymethlysilane) precursor, which has two ethoxy groups along with one methyl group attached to the silicon atoms, was used as precursor. The SiOCH film was deposited as a function of oxygen flow rates ranging from 0 to 100sccm. The deposition rate($AA$/min) of SiOCH film was increased due to the increase of oxygen radical as a function of $O_2$ flow rates. The dielectric constant was decreased from 3.0 to 2.77, as the film was annealed at $450^{circ}C$ for 30 min. So, it could account that the dielectric constant changes sensitively with $O_2$ flow rates. Also, the leakage current of the annealed film exhibited stable curve than that of asdeposited. These results were caused by the increase of Si-O-Si group and decrease of Si-CH group and OH group within the film by annealing.