Poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers possess excellent dielectric, mechan-ical properties and heat resistance. However, the surface of PBO fibers is smooth and highly chem-ical inert, resulting in poor interfacial compatibility to polymer matrix, which severely limits its wider application in high-performance fiber-reinforced resin matrix composites. In this work, ran-dom copolymers (P(S-co-BCB-co-MMA)) containing benzocyclobutene in the side-chain were syn-thesized by reversible addition-fragmentation chain transfer (RAFT) polymerization, which were then utilized to form dense random copolymer membrane on the surface of PBO fibers by thermally cross-linking at 250 ℃ (PBO@P fibers). Four kinds of synthesized P(S-co-BCB-co-MMA) with dif-ferent number-average molar mass (Mn) were well controlled and possessed narrow dispersity. When the Mn was 32300, the surface roughness of PBO@P fibers was increased from 11 nm (PBO fibers) to 39 nm. In addition, PBO@P fibers presented the optimal interfacial compatibility with bisphenol A cyanate (BADCy) resins. And the single fiber pull-out strength of PBO@P fibers/BADCy micro-composites was 4.5 MPa, increasing by 45.2％ in comparison with that of PBO fibers/BADCy micro-composites (3.1 MPa). Meantime, PBO@P fibers still retained excellent tensile strength (about 5.1 GPa). Overall, this work illustrates a simple and efficient surface func-tionalization method, which would provide a strong theoretical basis and technical support for con-trolling the surface structure&chemistry of inert substrates.