Abstract: The changes of the microstructure and properties of Al-20Si alloy after adding different content of Sb element were studied. The microstructure of the alloy was characterized by metallographic and differential scanning electron microscopy, and its tensile behavior and fracture mechanism were analyzed. The results show that with the addition of Sb element, the primary silicon in Al-20Si alloy has a metamorphic effect, which can cause the shape and size of the primary silicon change significantly. AlSb is acted as a heterogeneous core. The amount of the crystalline silicon increases and the tensile properties significantly improve.When Sb content reaches 0.8%, the size of primary silicon reaches the minimum, and the alloy has good comprehensive mechanical properties.The tensile strength and elongation of primary silicon increase from 93.2 MPa and 0.77% to 154.1 MPa and 1.97% without modification, increase by 65.34% and 155.84%, respectively.