Some statistical characteristics of signal and noise in shallow-water acoustical channel were analysed . Based on the differences in some statistical characteristics between the signal and the noise , the authors developed a new kind of signal processing technique-digital time correlative accumulation to operate sonar systems at a low data rate . Theoretical analyses and expermental results show . the false-alarm probability can be reduced to a low value of less than 10 -4 while the detection probability can reach a relatively high value of more than 0.9. By using the statistical averages of the multiple range detection value , the authors can greatly improve the accuracy of the detection . The method can be used for some other related fields, for example , ultrasonic detection in air medium . Some statistical characteristics of signal and noise in shallow-water acoustical channels were analysed. Based on the differences in some statistics characteristics between the signal and the noise, the authors developed a new kind of signal processing technique-digital time correlative accumulation to operate sonar systems Theoretical analysis and expermental results show. the false-alarm probability can be reduced to a low value of less than 10 -4 while the detection probability can reach a relatively high value of more than 0.9. By using the statistical averages of the multiple range detection value, the authors can greatly improve the accuracy of the detection. The method can be used for some other related fields, for example, ultrasonic detection in air medium.