Abstract: A 2-1/2D cylindrical full electromagnetic particle-in-cell code ABLE2D is used to simulate conducting and opening procession of a low-density plasma erosion opening switch. The building of computing model and complex boundaries has been introduced in detail. In simulation results, current channel forms at the generator side of the plasma at first and migrates to the load side of the plasma with current increase. The electrons in the current channel move across plasma from cathode to anode by E xB drift, the magnetic field is advected with the electron flow as a frozen in field tied to the electrons. The ion density is almost unchanged in the conduction procession of PEOS, but become lower quickly in the opening procession. When PEOS is entirely opening, ion density near cathode is close to