The purpose of this paper is to use the FiniteDifference TimeDomain (FDTD) method to study numerically t he resonant effects of FREMP into a cavity through a slot.　Computational data i ndicate that FREMP is easier to resonate with a cavity through a slot for the plentiful high frequencies of FREMP.　Because of the radiation outward，　the a mplitudes of resonant signals attenuate slowly. 