For A356 alloy, solidification with relative lower cooling rate will result in coarse grain size and lower mechanical properties. In this case, Al5Ti1B mater alloy was not the effective one to refine the A356 alloy. In present study, the effective grain refiner for A356 alloy was developed. Experimental results showed that the equiaxed grains were obtained with modified A356 alloy, rather than the dendritic grains of A356 refined by Al5Ti1B master alloy. Compared to the A356 alloy refined by 0.2wt.%Al5Ti1B, the yield strength, ultimate tensile strength and elongation of modified A356 alloy were increased by 4MPa, 30.6MPa, and 4.5% respectively. The value of yield strength, ultimate tensile strength and elongation of modified A356 alloy were 182.3MPa, 278.3MPa and 8.2%. The significant improvement of mechanical properties was ascribed to the effective nucleation of α-Al and the morphology evolution of eutectic Si.