A type of wide-band space-time constant modulus array algorithm for multi-user signal acquisition and interference suppression in underwater acoustic communication system is proposed to realize multi-user signal extraction and wide-band interference suppression. Compared with the conventional constant modulus array, it has stronger ability of multi-path and interference suppression. As an important part of cognitive underwater communication system, the time-frequency analysis and the instantaneous autocorrelation modulation algorithm for feature extraction provide an effective technique to classify the multi-user signals and interferences obtained by the wide-band constant modulus array, providing a solution to demodulation for different users and interference suppression. The performance of the cognitive processing structure is proved via numerical simulations.