In this work, carbon fibers were chemically modified with maleic anhydride through the Diels–Alder reaction under hydrothermal conditions, and then the modified carbon fiber reinforced phenolic resin composites were prepared by liquid impregnation processing. The structural and surface characteristics of carbon fibers were investigated by the Fourier transform infrared (FTIR) spectrum, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The tensile strength of the composites was measured by a universal material testing machine. The friction and wear behaviors of the composites were evaluated by a friction tester. Experimental results revealed that the carboxyl group was successfully grafted on the carbon fiber surface leading to the increase of surface activity without damaging the skin region and core region of the carbon fibers. The tensile strength of modified carbon fibers reinforced composites increased significantly by about 200%, while the wear volume decreased by about 50% compared with unmodified carbon fiber reinforced composites, resulting from good adhesion between the carbon fibers and resin matrix.