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Dielectric barrier discharge (DBD) is proved to be an effective method for surface treatment of polymers over the past 20 years and is now widely used in the fields of surface modification. In this paper, surface treatment of polyethylene terephthalate (PET) films for improving the hydrophilicity using DBD excited by unipolar nanosecond pulses is presented. Two typical discharges exhibiting homogeneous and filamentary modes are obtained under certain experimental conditions, and then, they are used to modify the surface of PET films. The microstructure and properties of the film surface before and after treatment are characterized with water contact angle measurement, scanning electron microscope, atomic force microscope, and X-ray photoelectron spectroscope. The results show that, with the treatment power density of 192 and 158 mW/cm2 in filamentary and homogeneous modes, respectively, surface morphology and property after treatment are significantly changed, and the physical etching and introduction of oxygen-containing polar functional groups account for the decease of surface contact angle and the increase of surface roughness. Compared with the filamentary DBD treatment, the homogeneous DBD (HDBD) is more effective in surface treatment, such as lower contact angle, higher roughness, and more oxygen-containing function groups after treatment. It is attributed to the fact that the HDBD can achieve a uniform treatment and can make the physical and chemical interaction much sufficient.