Abstract: The pitch-based carbon fibers were sized by the sizing agent of phenolic resin solution, and the single pitched-base carbon filber/epoxy resin composites were prepared using epoxy as a matrix. A single fiber fragmentation test, SEM and TG were performed to study the surface morphology of the carbon fiber before and after sizing interfacial properties of composites and the relationship between fracture length and interfacial shear strength. Results show that the interfacial properties of composites have improved on some appropriate concentrations of sizing agents. The uniformly sized composite with interfacial shear strength of 38.86 MPa could be gotten when the mass fraction was controlled at about 1%; the smaller the maximum probability of fracture length region or fracture length was, the higher the interfacial shear strength of composite was.