The invention discloses an automobile corrosion-resistant die-casting aluminum alloy and a preparation method thereof, and belongs to the field of aluminum alloy die-casting processing. The automobilecorrosion-resistant die-casting aluminum alloy comprises, by weight, 6.5%-7.6% of Si, 1.4%-2.1% of Mg, 0.8%-1.3% of Cu, 0.05%-0.11% of Sr, 0.4%-0.9%of Zn, 0.4%-0.8% of Mn, 0.2%-0.6% of Fe, 0.2%-0.5%of Y, 0.03%-0.05% of Er, less than or equal to 0.5% of other metals and non-metals, and the balance Al. The automobile corrosion-resistant die-casting aluminum alloy is prepared by the steps of melting, refining, standing, die casting, solid solution quenching treatment, aging treatment and the like. The aluminum alloy has the advantages that the corrosion resistance is greatly improved, the tensile property at high temperature is good, the toughness is high, and the extrusion resistance is good; and the preparation method is simple and feasible in process, and has the advantages of being highin safety and low in production process cost, and the produced aluminum alloy casting meets the use requirements of the workpiece needing to bear a large dynamic load.