Abstract: To detect underwater divers who are equipped with breathing apparatus,experimented and studied the rational of emitting acoustic signal by diver's breath,and proposed a passive detection method based on periodicity of diver's breath.Tank experiment got diver's periodic breath signal,demonstrated the possibility of passive detecting divers.Based on prominent frequency band of the diver signal,independently using Band-Pass-Filter(BPF) method and Matched-Filter(MF) method to get envelope signal and extract four features from envelope signal's spectrum for decision.Lake experiment in Sanya indicated that the four features had difference in detection distance and the farthest range was about 40 meters.Meanwhile,detection performance of MF method was better than BPF method.So it is concluded that restricted to energy level of radialization,the detection range is limited by passive method.