An　alumina　coating　with　a　thickness　of　100　mu　m　on　a　titanium　substrate　was　prepared　by　cathodic　micro-arc　electrodeposition.　The　microstructures　and　phase　compositions　of　the　coating　at　different　voltages　were　studied,　and　the　growth　mechanism　of　the　coating　was　analyzed.　The　results　show　that　the　coating　grows　by　the　following　steps:　the　stage　of　no　electric　spark,　micro-arc　discharge　and　local　arc　light.　In　these　courses　Al(NO3)(3)　is　dissociated　and　Al(OH)(3)　is　deposited　and　dehydrated.　The　high　temperature　and　pressure　produced　in　micro-arc　area　are　keys　to　the　formation　of　the　alumina　coating.　The　coating　is　mainly　composed　of　gamma-Al2O3　and　alpha-Al2O3.　The　content　of　alpha-Al2O3　is　increased　with　increasing　voltage,　which　amounts　to　76%　at　400V.