Abstract: An new method, which compresses the spectrum of the wideband / ultra -wideband LFM signal in radio channel to turn the wideband/ ultra -wideband signal into the narrowband signal, is presented in this paper. Using the inverse compression function, the compressed signal is reconstructed by nonlinear interpolation in digital domain. Moreover, the modulation slope and initial frequency of the original signal can still be estimated from the reconstructed LFM signal precisely. Computer simulation shows its validity.