Ni-Co-P / SiC composite coatings on Al alloys were prepared successfully by electroless plating technique.The surface morphologies, chemical composition, crystal structure, hardness of composite coatings were characterized and analyzed, whose corrosion resistance was investigated by electrochemical measurement . The results demonstrated that SiC nano particles can improve the hardness of Ni-Co-P alloy coating. Adding 12 g / L SiC nano particles into plating bath, the hardness of composite coatings may attain a maximum of 524 HV. In addition, Ni-Co-P / SiC composite coatings can also enhance the corrosion resistance of Al alloy materials. When SiC particle concentration is 9 g / L in plating bath, the corrosion resistance of composite coatings may be best relatively.