Abstract: Al-22Si-Cu alloy with different proportions of Sn was prepared by medium frequency induction casting. The influence of Sn content on the microstructure evolution of alloy was analyzed by experimental tests. The results show that there are many dendritic structures in the alloy. SDAS with a spacing of 10.12 μm was formed in alloy without Sn addition. When the Sn element was added, the secondary dendrite spacing of the alloy decreased.When Sn was not added, many large size eutectic silicon flakes were produced in the alloy matrix. With the addition of 1.2% Sn, the alloy formed finer eutectic silicon, which was still in lamellar form, but with significantly reduced lamellar size, forming many elliptic forms of eutectic silicon. In addition to α(Al) and Si, the primary phase of Al₂SiSn is generated in Al-22Si-Cu-1.2Sn alloy, and the primary phase and Al₂SiSn phase have the same unit cell parameters.