The mechanism forming of snow-shaped speckles on the worked-face of the castings of Al-Si Alloys was investigated by analyzing ZL104 and ZLl08 alloys etc. The snow-shaped speckles usually appear on the worked-face of the castings of AI-Si alloys whose macro-grain sizes are coarse. Microcosmically, the formation of snow-shaped speckles is related to large secondary dendrite arm spacings, which cause the uneven distribution of hard eutectic structure and soft a -Al dendrite. In terms of the factors that cause the snow-shaped speckles, it is practicable to preclude them by accelerating cooling rate or adding 2wt% Al5Ti1B to ZL104.