The silane coupling agent of ${gamma}$-aminopropyl triethoxy silane combined with ultrasonic vibration was employed to modify the surface of high modulus poly (p-phenylene-2, 6-benzobisoxazole) (HMPBO) fibers. The results showed that polar hydroxyl groups were successfully introduced on the HMPBO surface. The contact angles on HMPBO fibers both for water (${ heta}_{water}$) and for glycol (${ heta}_{glycol}$) gradually were decreased, and the surface roughness of HMPBO fibers was also increased. Meanwhile, the single fiber pull-out strength of HMPBO was increased accordingly.