Being used more and more widely in engineering, Al-Si alloys comprise about 80% of all kinds of aluminum alloys, which are the most widely utilized nonferrous alloys. Although most Al-Si alloys consist of multiple components, the eutectics in the structure accounts for 50%-90% of the sum volumeof such aloys. Therefore, understanding the modiifcation mechanism and function rules of the Al-Si eutectic solidiifcation is the technical key in controling the structures and properties of such casting aloys. The present paper chielfy reviews recent investigation developments and important conclusions along the lines of the functions of modification elements and their modification mechanism in the eutectic solidiifcation of Al-Si aloys.