Abstract: Magnetic leakage is described accurately by magnetic propagation equation on the boundary of magnetic dielectric and non-linear magnetization characteristic of different magnetic dielectric is considered, the distribution of steady, non-linear and forced axial symmetry magnetic field in magnetic fluid sealing device with different number of the poles is calculated by solving the partial difference equation described by magnetic vector potential, and unequally spaced net finite difference is adopted in the numerical calculation. This method overcomes the error caused by ideal estimation on magnetic leakage and work point of different place in magnetic dielectric in magnetic circuit method, the results are accurate, reasonable, reliable, and provide useful basis for structural design.