Abstract: The surface of F-12 fiber is modified by plasma grafting a kind of macromolecule grafting coupling agent. Based on the analysis of the modified surface of fiber by ESCA, the effects of molecular weight and concentration of grafting coupling agent on the transverse tensile strength are investigated, and the modification mechanism is analyzed according to fracture of transverse tensile. Results show that the grafting modification of grafting coupling agent can effectively improve the interfacial bond properties of F-12/ epoxy composite, and therefore increases the interlaminar shear strength and transverse tensile strength thereof.