The monomer Hexamethyldisilazane (HMDS) and oxygen gas were applied as the precursor and reaction gas, and the gas permselective materials were deposited on PET and chitosan substrate by plasma enhanced chemical vapor deposition (PECVD) method, respectively. Different reaction parameters such as monomer proportions, plasma input powers and deposition time were applied to prepare the film. The film properties were analyzed by surface profiler thickness test, Fourier Transform Infrared Spectroscopy (FTIR), water vapor transmission rate test (WVTR) and oxygen transmission rate test (OTR). The experimental results showed that plasma input power and monomer ratio influence the gas selective permeation (OTR/WVTR ratio) greatly; the technics can commendably improve gas permeation performance of the film. The mechanism of gas selective permeation of the film was preliminary discussed.