Abstract: Based on the micro-multi-phase structure model of molten alloys, the thermodynamics of the Al-Si molten alloy structure under electric pulse was analyzed, and the changes in matrix micro-hardness and solidifying point of the Al-22% Si alloy under electric pulse were studied. It is shown that electric pulse promotes the decomposition of Si particles in colloidal state in the alloy melt, improves the homogeneous degree of the melt, and eliminates the heredity from raw material partially. Electric pulse modification increases the super cooling degree of the Al-22% Si alloy melt and enhances the supersaturated degree of Si particles in the matrix, thereby increases the micro-hardness of the matrix. The variation in micro-hardness of the alloy matrix indicates that the alloy melt structure was sensitive to the change in electric pulse frequency.