The effects of adding a novel Al−3Ti−4.35La master alloy and Nd and heat treatment on the microstructure and mechanical properties of Al−7Si alloy were investigated. The results showed that the secondary dendrite arm spacing of α-Al in the as-cast Al−7Si alloy was refined from 18.3 to 11.9 μm after modification with 0.2 wt.% Al−Ti−La and 0.03 wt.% Nd, and the length of eutectic Si was reduced from 8.6 to 5.0 μm. After heat treatment at 535 °C for 3 h followed by 165 °C for 3 h, the morphology of the eutectic Si became more rounded, and the size decreased. The microhardness, ultimate tensile strength, and elongation were HV 66.1, 184.9 MPa, and 24.4%, respectively, which increased by 24.2%, 11.6%, and 194.0% compared to the as-cast state. The addition of Al−3Ti−4.35La master alloy and Nd can reduce the nucleation temperature of eutectic Si in Al−7Si, thereby suppressing its growth. Notably, the Ti₂(Al,Si)₂₀(La,Nd) phase formed in the Al−7Si alloy after the addition of Al−Ti−La and Nd adhered to or coexisted near the eutectic Si particles, inhibiting their growth.