This paper reports an analysis of the microstructure and property modifications on a commercial Mg alloy AZ91HP treated by using High Current Pulsed Electron Beam (HCPEB). It is shown that, a thin layer consisting of nanograined MgO formed on the top surface after HCPEB (electron energy ∼30 keV, pulse duration 1 μs, energy density ∼3 J/cm2) treatment, below which is a melted layer with depth of about 8–10 μm. The heat affected zone (HAZ) underneath the melted layer and stress wave affected zone contains many stress induced deformation marks. Meantime, a nearly complete dissolution of the intermetallic phase Mg17Al12 in the melted layer is observed, leading to the formation of a supersaturated solid solution on the surface. This is due to the solute trapping effect occurred during the fast solidification process. As a result, the wear and corrosion resistance of the alloy were significantly improved as shown by sliding friction, wear and immersion tests.