The present disclosure provides an aluminum alloy casing, a preparation method thereof, and a personal electronic device. The aluminum alloy casing includes an aluminum alloy matrix and an oxide film layer covering the surface of the aluminum alloy matrix, wherein the aluminum alloy matrix has a slit, the oxide film layer includes an inner anodic oxide film layer and an outer anodic oxide film layer, and the inner anodic oxide film layer has inner anodic oxide film layer nanopores; and the outer anodic oxide film layer has outer anodic oxide film layer nanopores.