Abstract: An accurate and effective sonar target echo model is a basis of detecting and recognizing sonar target, especially small scale target. In this paper, based on three parameter models of highlight echoes of sonar targets and the characteristic analysis in time domain for sonar target detecting and recognizing, the target echo model is optimized by using the parameter of echo time domain characteristic. Furthermore, a method of modeling broadband echo is proposed based on the algorithm of dividing frequency band in order to overcome the limitation that the single frequent detection method is unable to simultaneously consider both distance and precision in small target recognition,. The comparison of the echoes from simulation and anechoic tank test verifies the accuracy and validity of the echo models.