Abstract: Aluminum-silicon alloys have the advantages of high strength and toughness, good casting properties and mechanical properties, and are widely used in the manufacture of auto parts. The solidified structure of aluminum-silicon alloys is mainly composed of primary aluminum phase and eutectic silicon phase, and its mechanical properties mainly depend on the distribution and morphology of the two phases. The external magnetic field can enhance the flow of the melt during the solidification process, significantly affect the size, distribution and orientation of each phase in the alloys,and play an important role in improving the solidification structure of aluminum-silicon alloys. The effect of magnetic field strength on the microstructure and eutectic transformation mechanism of Al-7% Si hypoeutectic alloy was studied. The results show that under the action of external magnetic field, the eutectic transformation mechanism of the alloys does not change, but the misorientation between adjacent aluminum phases increases with the magnetic field strength increasing.