In the present study, the modification effect of Sr+Ce in Mg2Si/Al-Si-Cu composites was investigated for controlling both the microstructure and mechanical properties. Furthermore, the hardness and the abrasive resistance after modification were also studied. The results show that when the composites were modified by 0.40 mass% Ce, the morphology of the primary Mg2Si phase changes to a polygonal morphology with a size of 15 μm. However, in those with a 0.40 mass% Ce and 0.05 mass% Sr addition, the morphology changes to an irregular and equiaxed shape, and the size increases to 50 μm. Furthermore, in the 0.40 mass% Ce and 0.10 mass% Sr addition, the primary Mg2Si morphology transforms to a rectangular trapezoid, or “T” shape, with sizes measuring 70 μm. Additionally, in the 1.00 mass% Ce and 0.05 mass% Sr, and the 1.00 mass% Ce and 0.10 mass% Sr addition, the primary Mg2Si morphologies become either polygonal or irregular shaped, respectively. The eutectic phases change shows that, with the addition of Ce or Sr, the eutectic phases exist in the form of the binary eutectic of Al+Mg2Si or the ternary eutectic of Al+Mg2Si+Si. The hardness test illustrates that the hardness of the 1.00 mass% Ce and 0.05 mass% Sr and the 0.40 mass% Ce and 0.05 mass% Sr, modified composites are higher than the unmodified composites. The abrasive resistance data shows that modified composites with the 1.00 mass% Ce and 0.05 mass% Sr are higher than that of the modified and unmodified composites with a 0.40 mass% Ce and 0.05 mass% Sr. The abrasive resistance agrees with the hardness test results, and this demonstrates that the Sr+Ce addition can change the microstructure and enhance the mechanical properties of the material.