In this work, polyethylene terephthalate (PET) fibers were continuously treated by atmospheric dielectric barrier discharge (DBD) in Ar mixed O2 plasma, and the discharge was characterized by electrical function and optical diagnostics. It is found that the interfacial adhesion strength between treated PET fiber and resorcinol formaldehyde latex ( RFL) (little) -rubber was improved ( about 50 %) by the measurement of interfacial shear strength ( IFSS) and peel test. The wettability was improved rapidly in the initial treatment time. It is considered that oxidation chemical reaction as the major role of PET fiber surface modification is ahead of the physical etching effect. The high density of atomic oxygen in the plasma by optical emission spectroscopy supports the purpose. According to the scanning electron micrograph ( SEM ) image in the work, the longer treatment time obviously caused physical etching effect, which shall be less responsible for the improvement of the wettability.