AZ91HP magnesium alloy was treated by laser melting in vacuum. The results showed that with high power laser and rapidly scanning speed, the melted layers mainly consisted of α-Mg dendrite and lath-shaped β-Mg17Al12 distributing in the inter-dendrite, and the melted layer contained more β-Mg17Al12 than that of as-received Mg alloy. With the increase of laser powers, the grain dimension of the melted layer increased, and the increased amplitude along the long direction was 10 times of that along the width direction. Because of the grain refinement and the enhancement of the hard phase β-Mg17Al12, the microhardness of the melted layer was increased by 90%, the wear resistance was increased by 78%, and the corrosion resistance was significantly improved compared with as-received Mg alloy.