The invention discloses an aluminum alloy wheel gravity casting die and a casting method thereof. The aluminum alloy wheel gravity casting die comprises a cooling device, a top die, a side die, a bottom die and a die cavity formed by the top die, the side die and the bottom die; the bottom die is provided with a sprue spreader; the aluminum alloy wheel gravity casting die also comprises a heat insulation cup communicated with the die cavity and capable of storing molten aluminum, a pressing device capable of enabling the molten aluminum stored in the heat insulation cup to be continuously injected into the die cavity, and a plugging device capable of stopping the molten aluminum stored in the heat insulation cup from flowing into the die cavity under the action of gravity; the heat insulation cup is arranged on a rack of a gravity casting machine, and the plugging device is arranged on the bottom die or the rack of the gravity casting machine; and the casting method for the aluminum alloy wheel gravity casting die comprises molten aluminum injection, pressing, continuous casting, filling, feeding, crystallization and solidification. The cast aluminum alloy wheel has the advantages of a few dead heads, high weight and yield, and good quality stability.