Abstract: Using a 1D3V PIC code programmed by authors, the physical course of multipactor discharge suppressing on dielectric surface with different external magnetic field patterns is studied numerically. The secondary electron number, average electron energy, electron density, electron trajectories, transition time, static electric field and deposited power on dielectric surface are given in simulations. The numerical results could be concluded as follows: The mechanism of different external magnetic field loading patterns is not the same. For the normal direction external magnetic field loading, the rotation caused by external magnetic field disturbs microwave electric field accelerating electron course in order to decrease the impact energy which could suppress the multipactor discharge. For the parallel direction external magnetic field loading, the electrons are pushed out of dielectric surface in half microwave period which could not induce multipactor discharge, and the electrons are pushed in dielectric surface in the other half microwave period which could decrease the impact energy for suppressing the multipactor discharge. The resonant magnetic field condition is also discussed which could cause electron rotation radius and energy increasing continuously. The multipactor discharge suppressing effect could be improved by increasing the value of magnetic field for every external magnetic field loading pattern. It is easy to achieve loading but with higher value of magnetic field for normal direction external magnetic field. On the contrary, it is hard to achieve loading but with lower value of magnetic field for parallel direction external magnetic field.