The　Al-based　amorphous　and　nanocrystalline　composite　coatings　with　the　composition　of　Al-Ni-Y-Co　and　Al-Ni-Mm-Fe　were　prepared　on　AZ91　Mg-based　alloys　by　high　velocity　arc　spraying　technique　(HVAS).　The　structure　character　of　the　coatings　indicates　that　coatings　contain　the　mixture　of　amorphous　phases　and　crystalline　and　there　are　both　less　than　2%　porosity.　The　electrochemical　tests　of　the　coatings　and　the　substrate　were　studied.　The　coatings　show　the　passivation　ability　during　polarization,　but　AZ91　Mg-based　alloys　show　little　passivation.　The　corrosion　current　density　of　the　coatings　is　lower　than　that　of　AZ91　Mg-based　alloys.　The　results　show　that　the　coatings　have　an　excellent　corrosion　resistance　for　AZ91　Mg-based　alloys　in　5　wt%　NaCl　solution.