A method for making Mg(magnesium)-based intermetallic compound uses a thermal process during a melting process to produce largely the Mg-based intermetallic compound. The vapor pressure of Mg is high, thereby Mg is prone to be vaporized from a melt and a wrought solid alloy in the melting process of high temperature, for purifying the wrought Mg-based intermetallic compound. The method may simplify the process and devices for making the Mg-based intermetallic compound, and produce efficiently a larger of high purity Mg-based intermetallic compound.