Abstract: The influence of applied magnetic field on the process of vacuum flashover, especially on electric field-induced secondary electron emission and electron avalanche, has been investigated by a Monte-Carlo code based on single particle model. It is found that, the presence of applied magnetic field alters the motion of surface electrons, and then affects the distribution of surface charge, which finally influences the flashover voltage. Proper magnetic field applied on vacuum surface can inhibit the secondary electron avalanche, and thus enhances the flashover voltage. The effect of applied magnetic field on flashover depends on the field’s spatial distribution, and the near-cathode field is more favorable than the near-anode one.