Abstract: To study a new method that can jam the ultra-wideband(UWB) radar,which band-width is very wide,a new technique is introduced.The UWB radar is jammed by the comb spectrum signals in the new technique.The jam power is concentrated at some random frequency points between the radar signal band-width.In this way the jam power at some range is enhanced with increase the total jam power.And the coherence of the radar signal is destroyed.The jam principle is analyzed using the carrier-free UWB radar as the study object.Compared with the noise jam method,the simulated results prove that the technique is effective.