Graphene oxide (GO) was grafted onto the surface of carbon fiber (CF) by two synthetic routes with hexamethylene diisocyanate (HDI) tripolymer as the coupling agent. The first one was to use HDI tripolymer to modify the surface of GO, named GO-NCO, and then graft GO-NCO onto the oxidized carbon fiber surface. The other route was to use HDI tripolymer to modify the oxidized carbon fiber surface, named CFO-NCO, and then graft GO onto the CFO-NCO surface. The chemical compositions of the CF surface were confirmed by infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS). The surface morphologies of CF after modification and debonding from matrix were examined by scanning electron microscopy (SEM). The interfacial shear strength (IFSS) of CF/PA6 composites was also investigated by microbond test. It is found that the interfacial properties of GO modified carbon fiber reinforced polyamide 6 (CF-g-GO/PA6) composites are better by using the first route. The IFSS of CF-g-GO/PA6 composites reaches 61.4 MPa, is an increase of 40.2% compared with that of unmodified CF/PA6 composites. Moreover, the interfacial enhancement mechanism was further analyzed in detail. (C) 2018 Elsevier B.V. All rights reserved.