In this paper, atmospheric argon plasma was utilized to achieve surface cleaning and wettability modification of carbon fibers in aqueous solution. The morphology of fiber was characterized by scanning electron microscopy, surface chemical structure and composition were determined by fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, and water contact angle and tensile strength were also tested. The results show that plasma treatment can not only remove the size and impurities on the fiber surface, but also maintain the original surface morphology, and introduce a large number of oxygen-containing polar groups. Further analysis indicates that fibers exhibit the best performance when they are treated with plasma for 120 s, and the water contact angle of fiber can be reduced to 45.1°. Moreover, little influence has been found for the plasma modification on the mechanical properties of fibers, and the tensile strength of carbon fiber can still be kept at 3.23 GPa after 300 s plasma treatment.