Theoretical analysis shows that the migration behavior of a second phase during solidification processes in a high magnetic field (HMF) can be described by the migration velocity, which is a function of properties of melt matrix and the second phase, magnetic intensity and its gradient, as well as the geometry and size of the second phase. Lorentz force tends to make the second phase distribute homogenously, although its efficiency decreases with the increase of magnetic intensity beyond a certain value. When a gradient HMF is imposed, magnetization force becomes the dominant factor for the migration behavior of second phase. The effect of magnetization force increases with magnetic gradient, while it is difficult to control the migration of a second phase due to the constraint of Lorentz force when magnetic gradient is small. The theory has been experimentally verified by controlling the migration of in situ prepared particles in Al-Si and Al-Ni alloys under HMF conditions.