The surface of AZ31 magnesium alloy was treated by laser melting under pure argon atmosphere, and the microstructure, structure, and corrosion resistance of the ultra-thin AZ31 magnesium alloy surface melting layer prepared by low-power laser surface melting were studied through optical microscopy, scanning electron microscopy, and energy spectrum analyzer. The results indicated that the laser-melted layer exhibited a dense microstructure with grain sizes smaller than 20 μm. The surface microhardness increased from 5158 HV to 7478 HV after treatment. After laser melting treatment, the solid solubility of Al element in the microstructure of the melting layer increases, and there is a sensitivity to solidification cracks during the laser melting process. After laser melting and solidification treatment, the corrosion potential of magnesium alloy increased by 0.285 V compared to the matrix structure, and the corrosion current density decreased by one order of magnitude compared to the matrix magnesium alloy, resulting in a certain degree of improvement in corrosion resistance.