Surface of poly-p-phenylenebenzobisthiazole (PBO) fibers were activated by the coupling agent KH-560, and the surface of PBO fibers modified by coupling agent was treated with a coating containing heptafluorodecyltrimethoxysilane (HFTES). The surface structure and properties of PBO fibers were characterized by X-ray photoelectron spectroscopy and scanning electron microscopy. The effect of KH-560 on the surface modification of PBO fibers was investigated. The effects of HFTES mass fraction on hydrophobicity was studied. The results show that when the surface of PBO is treated with coupling agent KH-560, a thin layer of coupling agent coating is formed on the surface of PBO and the surface roughness of PBO fiber increases, and the epoxy group introduced on PBO fiber surface enhances surface activity of fibers. With the increase of HFTES concentration, the water absorption of PBO fiber decreases. The water absorption rate of PBO fibers treated with HFTES decreases significantly, and the water contact angle of PBO fibers treated with HFTES-containing silicone modified epoxy resin coating is 132°.