The work aims to study the method of preparing porous SiOx films based on plasma enhanced chemical vapor deposition (PECVD). With hexamethyldisiloxane (HMDSO) as monomer, the plasma was formed in the form of glow discharge with the addition of oxygen and argon and then small quantities of organic matters, so that they were deposited on the surface of the glass substrate and hence the silicon oxide films were prepared. By heat treatment at high temperatures, the carbon-hydrogen bonds and other organic components in the silicon oxide films were removed to form pores. The effects of experimental conditions, such as the ratio of monomer to oxygen, deposition time and deposition power on the deposition rate, morphology, structure and refractive index were investigated. When the discharge time was 10 min, the discharge power is 50 W, and the ratio of oxygen to monomer was 1︰6, the optimum deposition rate of the film was 14.6 nm/min. The absorption intensity of the stretching vibration decreased with the increase in the oxygen content. After heat treatment, the smoothness of the surface of the silicon oxide film had been improved, the morphology of the cross section had been changed after heat treatment, and the cracking of the cross section had appeared. SiOx films are deposited by PECVD and the porous SiOx films are prepared due to the porosity formed by heating, so that the dielectric constant can be reduced to below 1.9.