The invention relates to a Mg alloy anode material and a preparation method thereof, and belongs to the technical field of development and preparation of novel anode materials for high-power chemical power sources. The Mg alloy anode material can be utilized as an anode material for a seawater battery or an air battery, and comprises the following chemical components in percentage by mass: 4-7% of Al, 0.5-1.5% of Sn, 0.05-0.5% of Ce, and the balance of Mg and impurities, wherein the total content of the impurities is lower than or equal to 0.01%. A Mg alloy plate being good in electrochemical property, relatively low in self-corrosion rate and high in anode efficiency is obtained by subjecting the Mg alloy anode material to such metal material machining processes as smelting, heat treatment, extrusion and rolling. The Mg alloy anode material provided by the invention has the advantages that the component design is reasonable, the preparation process is simple, the properties of the obtained product are good, and the large-scale industrialized application is facilitated.