In the world of beverage market, polyethylene terephthalate (PET) bottle is one of the most useful containers for lightweight, optically transparent, unbreakable and recyclable characteristics. There exist great difficulties in the application of PET bottles in the package of beer and wine etc. Thus, gas-barrier enhancement technologies have been paid more attention. In this investigation, gas barrier property of PET has been improved by plasma enhanced chemical vapor deposition (PECVD) and plasma immersion ion implantation (PIII) technologies. Gas permeability tester and mechanical folding device were developed to study the barrier property and deformation failure behaviors. The surface characterization, chemical structure, optical, mechanical properties of PET coated with DLC have been investigated by X-ray photoelectron spectroscopy (XPS), contact angle measurement, light transmission analysis, nanoindentation and friction wear tests. XPS data reveals that carbon layer deposited on PET contains small fraction of sp3 and the ratio of sp3/sp2 is about 1/10. The enhancement of water wettability, better optical transparency, and higher wear resistance have been found after the samples were treated under high RF power, bias voltage and gas pressure conditions. The wettability and wear resistance of the samples implanted by hydrocarbon ion are better than those treated by nitrogen ion. However the optical transparency becomes worse. Surface hardness of PET increases obviously by C implantation/deposition due to formation of hard layers while wear-resistance may be improved with nitrogen incorporation. Mechanical folding test was applied to analyze the crack behavior of DLC films. The results show that the crack appears due to the mechanical stress and the initiation and propagations of the cracks may be suppressed with higher RF power, bias voltage and gas pressure. The nitrogen incorporation may decrease the crack growth. For the nitrogen-implanted samples, the initiation of crack is greatly delayed, and crack spacing interval is small. The samples prepared by PECVD and PIII technologies have been investigated using homemade gas permeation tester.