The invention discloses a machining method of a vacuum booster shell of a magnesium-aluminum alloy. Proper raw materials are selected; pressing force P in each drawing procedure of workpieces and pressing force P' in each shaping procedure of the workpieces are precisely calculated; then, analog models are built in analysis software for simulation analysis to determine precise deformation in eachpunching procedure; punching molds in each procedure are manufactured according to analysis results for trial production and adjustment according to punching conditions until qualified products are produced; and then, the large-batch punching production is performed. The machining method can guarantee machining of high-quality magnesium-aluminum alloy booster shells, and realizes lightness of thebooster shells; and the magnesium-aluminum alloy shells produced by the method are high in yield, so that the product production cost is greatly reduced. The invention further discloses a punching mold structure of the shells.