The invention discloses a metal aluminum base aluminum nitride package substrate and a preparation method thereof, and belongs to the field of microelectronic materials. The package substrate comprises a metal aluminum base, a porous anodic alumina film formed on the surface of the metal aluminum base, and an aluminum nitride film formed on the surface of the anodic alumina film, wherein the porosity of the anodic alumina film is reduced gradually along the direction from the metal aluminum base to the aluminum nitride film. According to the preparation method of the package substrate, metal aluminum is used as the base, anodic oxidation is carried out on one surface of aluminum to generate a layer of the porous anodic alumina film, and then the aluminum nitride film is deposited on the anodic alumina film in a vacuum mode. According to the metal aluminum base aluminum nitride package substrate, the anodic oxidation is carried out on the metal aluminum base, an anodic alumina thermal stress buffer layer with a coefficient of thermal expansion gradually varied is formed between the aluminum base and the aluminum nitride film, thermal shock resistance is improved obviously, cracking does not occur under 300 DEG C thermal shock, and therefore the metal aluminum base aluminum nitride package substrate can be applied in a subsequent process of semiconductor chip package well.