The liquid phase separation behavior and the evolution of the solidification microstructure of a binary Cu50Fe50 alloy were investigated under the conditions of without and with a 10 T magnetic field, with different undercooling during the solidification process. Results show that the combined effect of Stokes motion and Marangoni convection leads to the formation of the core-shell structure under the condition without the magnetic field. In addition, specific gravity segregation is reinforced by increasing the undercooling, resulting in Fe-rich phase drifts towards the sample edge. In the 10 T magnetic field, the Fe-rich phase is elongated in the parallel direction of the magnetic field under the action of demagnetization energy due to the difference of static magnetic energy and surface energy. In the vertical direction, through the action of Lorentz force, the convection in the melt is inhibited and Fe-rich phase becomes more dispersed. Meanwhile, the diffusion of the two phases and the coagulation of the Fe-rich phases are also restrained under the magnetic field, therefore, the phase volume fraction of the Fe-rich phase decreases at the same undercooling in the 10 T magnetic field. The magnetic field inhibits the segregation behavior in the vertical direction of the magnetic field, and at the same time, improves the gravitational segregation to a certain extent, which has a very important impact on microstructure regulation.