Inspired by mussel heuristic chemistry, a novel method for improving surface wettability and adhesion of carbon fibers with epoxy resins was proposed by codepositing gallic acid and polyethylene imine on the carbon fiber surfaces in a convenient operation. The results of scanning electron microscopy, infrared, Raman and X-ray photoelectron spectra revealed that gallic acid and polyethylene imine could undergo Michael addition or Schiff base reaction and codeposit on the carbon fiber surfaces successfully. The gallic acid-polyethylene imine codeposited carbon fibers were used to fabricate epoxy matrix composites. The results of mechanical tests showed that interlaminar shear strength, flexural modulus and strength of the gallic acid-polyethylene imine codeposited carbon fiber composite were increased by 27, 38, and 27% respectively, compared with those of the untreated carbon fiber composite. The conclusion can be drawn that the gallic acid-polyethylene imine codeposition is an effective method for improving interfacial properties of carbon fiber reinforced epoxy resin matrix composites.