Abstract: The PET fiber was treated by oxygen plasma combined with hydrophilic agent,and the influence of plasma on structure and properties of PET fiber were studied.The results showed that oxygen plasma treatment etched the fiber surface and the oxygen-containing groups were introduced to the chain of the molecule,thus wettability of the PET fiber was improved.But when the treatment time exceeded 3 minutes,the polarity groups were broken,resulting in decline in its wettability.The hydrophilicity and the hydrophilicity durability were improved dramatically when the PET fiber treated by plasma was finished by hydrophilic agent.FT-IR spectrum indicated the carbonyl oxygen-containing groups had been induced onto the PET fiber and the mechanical and thermal properties were not affected after oxygen plasma treatment.