An　Al-Ni-Y-Co　amorphous　and　nanocrystalline　composite　coating　was　prepared　on　the　surface　of　the　AZ91　Mg　alloy　by　using　an　automatic　high　velocity　arc　spraying　system.　Its　microstructures　were　analyzed　by　scanning　electron　microscope　(SEM),　X-ray　diffraction　(XRD)　and　transmission　electron　microscope　(TEM).　The　results　show　that　the　coatings　compose　of　amorphous,　nanocrystalline　and　microcrystalline　phases,　which　has　a　compact　structure　with　low　porosity　about　1.8%.　The　average　Vickers　microhardness　and　bond　strength　of　this　coating　are　311.7　HV0.1　and　26.8　MPa.　Its　relative　wear　resistance　is　about　10　times　than　that　of　Al　coating　and　6　times　than　that　of　AZ91　magnesium　alloy.　The　corrosion　potential　of　this　coating　is　more　positive　than　that　of　Al　coating　and　AZ91　magnesium　alloy,　and　the　corresponding　corrosion　current　density　value　is　about　1/2　the　same　as　that　of　Al　coating　and　1/5　as　that　of　AZ91　Mg　alloy.　Especially,　compared　with　the　surface　on　corroded　Al　coating　and　AZ91　Mg　alloy,　the　corroded　Al-Ni-Y-Co　coating　has　a　more　flattered　surface　with　less　corrosive　piting　than　Al　coating.　It　is　confirmed　that　the　Al-Ni-Y-Co　coating　is　an　excellent　coatinig　with　higher　wear-resistance　and　corrosion　resistance.