The methods of argon plasma and argon plasma combined with coupling agents were employed to modify the poly[1,4-phenylene-cis-benzobisoxazole] (PBO) fiber surface. The interfacial shearing strength (IFSS) of PBO fibers/epoxy resin was measured by the single fiber pull-out test. The surface chemical structure and surface composition of PBO fibers were determined by FTIR and X-ray photoelectron spectroscopy (XPS), respectively. The morphology of the fiber surface was investigated by scanning electron microscopy (SEM) and the specific surface area of the fibers was calculated by B.E.T. equation. Furthermore, the wettability of PBO fibers was confirmed by the droplet profile analysis method. The results showed that the elemental composition ratio of the fiber surface changed after the modification. The IFSS increased by 42% and 78% when the fibers were treated by argon plasma and argon plasma combined with the coupling agents, respectively. Meanwhile, the specific surface areas of the treated fibers were improved. In addition compared to the modification of argon plasma, the modification of argon plasma combined with the coupling agents inhibited the attenuation phenomena of the IFSS and the wettability