Abstract: The effects of mixed rare earth RE on the microstructure and mechanical properties of A356 alloy were studied. The results show that when the RE adding amount is 0.5 wt%, the eutectic silicon of the alloy changes from coarse schistose to fine granular, and is distributed evenly in the alloy matrix, the tensile strength of the alloy is 200.8MPa袁the elongation is 4.52%袁and the Brinell hardness is 58.6HBW. The tensile fracture mode of the cast alloy is mixed fracture with ductile fracture dominated by dimples and cleavage brittle fracture. When the addition amount of RE is 0.9%, slight over-modification begins to appear in the alloy. At this time, the eutectic Si begins to coarsen and grows up slightly, and there is a tendency of segregation in some regions, but the morphology is still granular.