A kind of Zr, Sr composite microalloying and Mg alloying high hardness corrosion-resistant Al-Si-Cu cast aluminum alloy, it is characterized in that described aluminum alloy is mainly made of aluminum (Al), silicon (Si), copper (Cu ), magnesium (Mg), zirconium (Zr), strontium (Sr), and iron (Fe). The preparation method sequentially includes: (1) melting pure Al and Al-Si master alloys and raising the temperature to 850°C, and then sequentially adding Al-Cu, Al-Zr and Al-Sr master alloys; (2) waiting for all the master alloys After the alloy and metal are melted, adjust the temperature to 750°C, add pure Mg, and after it melts, add hexachloroethane for refining and degassing until no gas escapes, keep it for 5-10 minutes, then remove the slag and cast it into an ingot. The aluminum alloy of the present invention has a dense as-cast structure, an average unnotched impact toughness at room temperature of 16.35J / cm2, a tensile strength of 262.132MPa, and an elongation of 5.645%. At the same time, when it is immersed in a 3.5% NaCl aqueous solution at a temperature of 37°C for 93 hours The uniform corrosion rate is 0.321081508mm / y.