The present invention relates to a cast aluminum alloy used for high power density pistons and a preparation method thereof, wherein, a cast aluminum alloy is characterized in that: in terms of mass percentage, the cast aluminum alloy comprises the following components: Si: 11.0 ~12.6%, Cu: 3.5~4.5%, Mg: 0.7~1.2%, Ni: 2.2~3.2%, Fe: 0.6~0.8%, Mn: 0.25~0.35%, Sc: 0.10~0.15%, Zr: 0.13~ 0.17%, Ti: 0.13-0.17%, V: 0.08-0.12%, and the balance is Al and unavoidable impurities. Heat-resistant aluminum alloy is based on the thermodynamic analysis of the material system, microstructure control and experimental testing, by appropriately increasing and adjusting the relative addition of elements such as Fe, Ni, Cu, etc., to increase the 350‑420 °C high temperature support strengthening phase Al 9 FeNi, Al 15 Si 2 (Fe,Mn) 3 、Al 3 CuNi, Al 7 Cu 4 The content of Ni makes the solidification structure present scattered network, petal and diffuse stripe distribution. These high-temperature strengthening phases can hinder the grain boundary slip and dislocation movement in the alloy, and improve the heat resistance and grain boundary. Strength and creep resistance.