Abstract: The interfacial properties between polymer and fiber are particularly important for improving the mechanical properties of composites. In this paper, the surface of nano-SiO₂ was modified by polyurethane (PU) capped by isocyanate (—NCO), and the surface of carbon fiber (CF) was modified by KH550. Because of the high reactivity of —NH₂ and —NCO, the covalent bond was formed between CF and nano-SiO₂ particles through PU molecular chain. The results showed that the introduction of PU polar molecular chain improved the surface energy and wettability of CF. Compared with the CF directly grafted with nano particles by KH550(CF-KH550-SiO₂), the surface energy of the CF with nano particles linked by PU (CF-KH550-PU-SiO₂) molecules increased by 23.0%, and the grafting rate and dispersion uniformity of surface nano SiO₂ particles also improved significantly. Compared with the untreaed CF/epoxy resin (EP) composites, the interfacial strength (IFSS) and the interlaminar shear strength (ILSS) of CF-KH550-PU-SiO₂/EP composites increased by 72.9% and 47.9% respectively. Compared with the CF-KH550-SiO₂/EP composites, IFSS and ILSS of CF-KH550-PU-SiO₂/EP composites increased by 17.3% and 11.2%, respectively.