Abstract: A 130nm bulk PMOSFET is generated and calibrated with TCAD(Technology Computer Aided Design) simulator.Single event simulation is used to investigate the impact of guard-ring with different widths on parasitic bipolar effect due to a direct hit ion strike in VDSM device.Simulation results demonstrate that guard-ring structure can significantly reduce SET(Single Event Transient) current pulse width,effectively suppress the parasitic bipolar charge collection,the capacity of this suppression is enhanced with the guard-ring becoming widen,and tends to be stabilized ultimately.In order to consider the area of harden device and the irradiation resistance simultaneously,guard-ring structure is improved.As the guard-ring with width of 0.38μm,it is proved that novel structure can maintain the single event resistance of the device with area dropping by 29.4%.