The invention relates to cast aluminum alloy capable of being anodized and a preparation method thereof. The cast aluminum alloy capable of being anodized is prepared from, by weight, 0.8%-2.0% of Si, 0.8%-3.0% of Mg, 0.1%-0.8% of Mn, less than 0.3% of Fe, less than 0.3% of Cu, less than 0.3% of Zn, less than 0.05% of at least one of the trace elements including Ti, B, Re and Zr, and the balance Al. The preparation method comprises the steps that firstly, smelting is conducted, then degassing and refining are conducted, the smelting temperature is adjusted, hexachloroethane is added for degassing and refining, and purifying and slagging-off are conducted; secondly, modification and secondary refining are conducted, the smelting temperature is adjusted to be 730-750 DEG C, an Al-Sr modificator is added for modification treatment, the smelting temperature is adjusted to be 700-720 DEG C, degassing and refining agents are added, and slagging-off is conducted; and finally, pouring and casting are conducted. By the adoption of the cast aluminum alloy capable of being anodized and the preparation method thereof, the oxidation effect is more excellent, a film is thick, and the color and luster are uniform; by controlling the contents of the main alloy elements, the cast aluminum alloy has high strength and formability.