The invention relates to a method for optimally die casting an aluminum alloy by adopting rare earth and a modified alloy, and belongs to the field of metal. The method for optimally die casting the aluminum alloy comprises the steps that a rare earth yttrium or a rare earth gadolinium is taken as a modifier, and the aluminum alloy and the modifier are molten. The rare earth yttrium or the rare earth gadolinium is added into the alloy through a melting mode, and the microstructure morphology of the alloy can be improved and adjusted, so that the mechanical properties of the alloy can achieve anticipant adjustment.