Magnetic-electrochemical compound polishing is applied in difficult-to-process materials little by little. The influence of the magnetic field to electrochemical process is very complicated. In the paper, using Coulomb laws and Lorentz force, the two kinds of math model of the movement of the charged particles are established according to the different magnetic field whose direction is vertical or parallel to the electrical field. The velocity equations and loci equations of three typical particles are concluded in two kinds of magnetic field’s directions. To be compared and analyzed carefully, the influence of the magnetic field’s direction to polishing is concluded. This study can guide how to determine the magnetic field’s direction in magnetic-electrochemical compound polishing, and build the theoretical basis to study the mechanism of magnetic-electrochemical compound polishing.