Abstract: By analyzing the characteristics of animal sonar signals, it's pointed out that they are a kind of hyperbolic frequency-modulated (HFM) signal. HFM signals provide the spread-unvariation in both Doppler and delay, and minimum time-frequency coupling and smearing in detection or classification of the object echoes. To meet the requirements of modern torpedo, the animal sonar signals with different parameters are simulated and the narrow-and wide-band ambiguity and the Wigner-Ville distributions are shown graphically.