Amorphous SiCOF films with a low dielectric constant and good moisture resistance were deposited in a plasma-enhanced chemical vapor deposition (PECVD) system using a C4F8/TEOS/O-2 mixture. The dielectric constant can be reduced to 2.6 when the flow rate of C4F8 increases to 30 seem. The breakdown strength of the deposited film can be improved by increasing the C4F8 flow rate. Through Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses, the structural changes caused by C doping are discussed in detail. There are C-F bonds and cross-link C-C bonds, in addition to Si-O and Si-F bonds, in the films. It was found that carbon dopant in the film results in a decrease in the Si-O-Si bond angle and an increase in the Si-O bond length. These changes are relative to the redistribution of partial charge on Si-O-Si due to carbon doping. Furthermore, the C-F bonds in a-SiCOF film will reduce Si-OH components in the film and improve the moisture resistance of the film due to the hydrophobic property of the C-F bond.