Abstract: Passive acoustic monitoring has become an important means to study dolphin acoustic signal. In order to increase calculation speed and detection rate of the monitoring system and reduce power consumption for its longterm work, a fast detection method of dolphin echolocation signals based on the time-domain characteristics is proposed in this paper. This method does not need FFT transformation and frequency domain analysis, so as to greatly improve the calculation speed and effectively reduces the computational consumption, thereby to prolong the working time and improve working efficiency of the system. Tests for the system are conducted by using dolphin acoustic signal data collected in the field and indoors, and the results show that the detection speed is greatly improved, and the accuracy rate reaches more than 90%.