Abstract: Based on plasma explosive emission model, the self c onsistent and 21/2 dimensional electromagnetic particleincell code is employed to simulate the characteristics of a magnetically insulated ion dio de for intense pulsed ion beams. The trajectories of electrons and protons in th e anodecathode gap of the diode, the timedependence of the diode current I d, the electron loss current density to anode je and the extracted pro ton current density jp are presented at externally insulating magnetic fie ld in the range of 2Bcrit and the maxiumum diode voltage of 300 kV. Th e effects of the magnetic field on the virtual cathode, the diode impedance as w ell as the overall ion current efficiency of the diode are discussed.