Fine Al2O3 coating could be obtained from alumina sols modified by chelator acetylaceton, under exact control of the parameters. Al2O3 coating by the sol-gel method on the carbon-fiber (CF) surface was investigated in detail to improve the oxidation resistance of CFs. Further study focused on making the Al2O3-coated fiber reinforced aluminum composite prefabrication. XRD, IR, TG-DTA, and SEM methods were used to analyze the alumina gels, the coated CFs, and the prefabrication. After the coating treatment, the oxidation resistance of the carbon fibers is enhanced, the wetting between the fibers and melting aluminum is greatly improved, and the tensile strength of CF/Al prefabrication is heightened.