The invention relates to a preparation method of an aluminum alloy. The preparation method comprises the following steps of 1, preparing raw materials; 2, smelting raw materials in a smelting furnace,placing aluminum in the lowermost layer when the raw materials are put into the smelting furnace, smelting and melting the raw materials of aluminum, silicon, copper, yttrium, silicon, chromium, carrying out temperature measurement on the mixture, adopting a slag removal device to remove dross on the surface of a molten liquid when the temperature reaches 825-855 DEG C, then adding magnesium according to the weight ratio, stirring the molten liquid in the furnace for 10-15 minutes by using a stirring device, then using a metallurgical slag removal device to remove slag again, then adding theraw materials of cadmium, ytterbium, samarium and terbium, stirring for 20-30 minutes, using a bell jar to press the hexachloroethane to carry out degassing and deslagging, carrying out standing for 20-30 minutes, carrying out slag removal and filtration to obtain an aluminum alloy melt; 3, finishing; 4, casting and extruding and forming; 5, homogenizing annealing treatment; 6, cooling; and 7, carrying out heat treatment. According to the method, the mechanical property of the alloy is improved by virtue of a reasonable extrusion and heat treatment process, so that the tensile strength of thealuminum alloy reaches more than 370 MPa.