In order to find the effects of high magnetic fields on the solidification processes of metallic materials, the changes of solidified structures of Al-14.98% Si and Al-9.2% Si alloys were examined in this study. The alloys were solidified under different magnetic field conditions, and then the distribution and morphologies of Si element in the solidified structures was analyzed. It is found that uniform magnetic fields and gradient magnetic fields can affect the solidified structures of the alloy by Lorenz force and magnetization force respectively, and the imposed magnetic fields also can change the distribution of primary Si crystals in the alloy remarkably. The primary Si crystals distributed homogeneously under uniform magnetic field conditions, while they congregated at the upside or downside of samples by the combined action of buoyancy and magnetization force under gradient magnetic field conditions. Furthermore, the morphologies of eutectic crystals in the alloy were changed by the magnetic fields and the layer thickness of eutectic crystals were different at the upside and downside under gradient magnetic field. Both theoretical analysis and examinations indicated that magnetic energy also affected the solidifying process, the content of eutectic aluminum in eutectic structure increased and eutectic point left-shifted when Al-Si alloy solidified under high magnetic fields.