The nano-thickness SiOx deposited on polyethylene terephthalate (PET) film and biaxially oriented polypropylene (BOPP) were fabricated by plasma enhanced chemical vapor deposition (PECVD) in a radio frequency (13.56 MHz) glow discharge. The nano-coatings were characterized by using Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and ultrasonic atomic force microscopy (UAFM). With AFM and UAFM, the topography and ultrasonic amplitude images were obtained. In particular, the UAFM images reveal the subsurface defects in the coating. The tensile property, contact angle and OTR of the PET present and absent of the SiOx coating were investigated experimentally respectively. The results can show that the SiOx coating can improved the barrier and the tensile strength.