Abstract: To understand the interference and damage effect of ultra-wideband electromagnetic pulse (UWB-EMP) on a typical radio fuze, the coupling effect of typical cavity was researched based on time domain finite integral method (FIT). Taking the cavity of typical radio fuze and low-frequency printed circuit board (PCB) as simulation model, the influences of aperture parameters, pulse parameters and PCB in cavity on coupling effect were analyzed. The results show that the coupling coefficient of rectangular aperture is affected by polarization direction obviously compared with those of circular and square apertures, and the coupling coefficient increases with the decreasing of UWB pulse rise time. Furthermore, the coupling coefficient decreases and resonance frequency changes after inserting a PCB into the cavity of the fuze.