The ultra-wideband (UWB) scattering characteristics of targets are computed by using the method of FDTD with Unsplit-field Perfectly Matched Layer (UPML) boundary condition. UPML absorbing boundary condition needs less storage by introducing auxiliary equations. The ultra-wideband bistatic RCS of F117A fighter is computed in this paper. The computation results are compared with the results in Ref. 1 and both accord with each other well.