The invention relates to an extrusion die casting method for a thin-walled aluminum alloy automobile engine pump body cover, and the method is suitable for obtaining the automobile engine pump body cover which is good in airtightness and compactness, high in product percent of pass, complex in shape and structure and thin in wall. The extrusion die casting method includes the steps that a quantitative pouring cup is adopted to convey aluminum alloy liquid from a heat preservation furnace to a die-casting machine cylinder chamber, an extrusion die-casting machine punch pushes the aluminum alloy liquid steadily to a die cavity, and the aluminum alloy liquid pushing process sequentially includes three stages, namely the extrusion die casting speed, the die casting speed of a horizontal die-casting machine and pressure maintaining, shrink compensation and particle compaction, wherein in the first stage, the pushing range accounts for 50-60% the whole range, so that air in a material cylinder escapes, the alloy liquid enters the middle segment of the die cavity at a low speed, air escapes, and air trapping is reduced; in the second stage, the pushing range accounts for 33-43% the whole range, so that press-shoot is conducted rapidly, a product is fully formed in an inflatable mode, and cold shut is solved through rapid formation; in the third stage, a blank casting is obtained.