Abstract: The relation between three main factors (waveform, channel and receiver) of active sonar is discussed in this paper. The models of active sonar channel, which include marine reverberation, signal propagation and object scattering in sonar processes, are described, by generalized scattering function and generalized coherence function. Physical significance and measuring method of both function are explained with aid of channel output corralation function and matched filter output. Finally, the fundamental principles for design of the optimum waveform and the optimum receiver are presented.