Abstract: An efficient method is proposed for the realization of high resolution spectrum estimation and weak signals detection in broadband reconnaissance receiver. The broadband input signal is first divided into several equivalent narrow bands using digital channelized receiver, and the subband spectrums formed by FFT respectively is ranked to recompose the whole spectrum of the input signal. Noise floor is estimated by morphologic operation to correct the spectrum. Signal detection is performed by comparing the corrected spectrum line and the adaptive threshold estimated based on the distribution characteristic of the noise spectrum lines. Analysis and simulation results show the effectiveness of the proposed method.