In traditional casting of Al-Si alloys, the coarse dendritic α-Al phase and acicular eutectic Si strongly split the matrix, significantly compromising the mechanical properties. To refine the microstructure of Al-Si alloys and enhance their mechanical performance, the investigation focused on the influence of different additions of Y/Al-5Ti-1B modifiers (with Al-5Ti-1B held constant at 2 wt. %, and rare earth element Y varied at 0.05 wt. %, 0.1 wt. %, 0.2 wt. %, 0.3 wt. %, 0.4 wt. %, 0.5 wt. %) on the microstructure and mechanical properties of Al-7Si alloy was conducted by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and a universal materials testing machine. Furthermore, the modification mechanisms of Y/Al-5Ti-1B on an Al-7Si alloy were also explored. The results demonstrate that the optimal modification effect is achieved with 2 wt. % Al-5Ti-1B and 0.4 wt. % rare earth Y. The coarse needle-like eutectic Si transforms into fine granular structures, with lengths and widths reduced to 2.7 and 0.8 μm, respectively. This represents significant decreases of 90.6% and 4.7%, respectively, compared to those of the unmodified alloy. The ultimate tensile strength (UTS) increases by 24.4% from 168.1 MPa to 209.1 MPa, while the elongation (EL) increases by 54.4% from 6.23% to 9.62%. The fracture mode of the alloy transforms from a typical brittle fracture to a ductile-brittle mixed fracture.