The invention belongs to the technical field of aluminum alloy casting and particularly relates to a preparation method for high-strength cast aluminum alloy. The problems that in the prior art, aluminum alloy castings are low in structure compactness, prone to segregation and poor in casting strength, toughness and plastic overall performance are solved. The preparation method comprises the following steps that Si, Mg, Zn, Cu, Mn, Ti, Re and Sn are added into a metal smelting furnace and subjected to high-temperature melting, and alloy melt A is obtained and subjected to heat preservation for standby use; after Al is melted at a high temperature, a refining agent is added for refining, and pure molten aluminum B is obtained; the alloy melt A is added into the pure molten aluminum B, SiC and a modificator are added and mixed evenly, and alloy liquid C is obtained; and casting of the alloy liquid C is completed at a high temperature, and castings are obtained. The structure compactness of the castings is effectively improved, the casting segregation problem is avoided, and the obtained aluminum alloy has high strength and hardness, and is good in abrasion resistance, corrosion resistance, machinability and casting performance and wide in application prospect.