The Al-40Si alloy modified by 0.5 wt% Sr addition was heat treated using L9(34) orthogonal test. The mechanical properties were measured. The microstructures were analyzed using optical microscope. After heat treatment, the extension percentage increases more than twice. The eutectic matrix and primary Si phase are both refined. The primary Si phase is refined and homogeneously distributes in the matrix with the solution temperature and time increasing. However, the primary Si phase agglomerates each other with further increasing of the solution temperature and time. According to the microstructure, the optimal solution temperature and time are 500 °C and 14 hours, respectively. In addition, the optimal values for the hardness, tensile strength, and extension percentage are 35.4 HRC, 82.2 MPa, and 2.05 %, respectively.