Abstract: The recognition of the digital radio frequency memory(DRFM) jamming is the precondition to jamming suppression of radar. To radar linear frequency modulation(LFM) signal, the slice difference of the fractional Fourier transform(FrFT) and short Fourier transform(SFT) in U domain is proposed to detect and discriminate the dense repeater jamming. The approximation of the slices of LFM signal repeat jamming in the U domain is adopted to accomplish the detection and discrimination and its efficiency is proven by computer simulation.