A continuous coaxial atmospheric pressure dielectric barrier discharge plasma system (PLA-PLA) was used to modify the surface of PAN-based carbon fibers. The influence of plasma parameters on the surface of carbon fibers was investigated with respect to gas flow ratio and treatment time. The surface morphologies of carbon fibers before/after plasma processing were determined by scanning electron microscope (SEM), and the surface chemical composition of the fabric samples was analyzed by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The contact angle and tensile strength of the carbon fibers were also tested to investigate their wettability and mechanical properties. The results indicated that a large amount of reactive functional groups were introduced into the carbon fibers surface after the oxygen plasma treatment. In addition, the tensile strength of the treated fibers dropped little.