In order to improve the detection performance of small-scale underwater targets in a shallow-water reverberation-limited environment, broadband linear frequency-modulated （LFM） signals containing vast target information and weak reverberation background correlation are used to perform a time-frequency spectrogram reassignment and a matching detection for the target broadband echoes. Then, the time-frequency features of target echo respectively obtained by the short-time Fourier transform （STFY） and by the wavelet scalogram reassignment are compared, finding out that the reassignment helps to effectively separate the target signal and the coupled reverberation signal. Moreover, a time-frequency matching detector based on wavelet scalogram reassignment is designed according to the matched filter features. Simulated and test results indicate that the proposed method is superior to the traditional matched filtering method with a gain increase of about 4 dB, and that it can accurately locate the underwater targets in reverberation-limited area with strong side-lobe suppression.