With widely using difficult-to-process materials, such as the stainless steel and SnSb alloy, the magnetic-electrochemical compound polishing process has been paid much more attention by some Japanese and Chinese researchers. In the paper, the math model of the movement of the charged particles in a magnetic field is established through the analysis of its movement process, using Coulomb laws and Lorentz force. The velocity equations and loci equations are concluded, and the movements of there typical particles are compared carefully and analyzed. Therefore, the function of the magnetic field is drawn. In the end, to verify the model, the magnetic- electrochemical compound polishing process were tested and the results were compared with those obtained from the model, the results showed the movement model was reasonable and the analyzing to function of magnetic field was correct.