Abstract: Theory of the article was applied in research of the echo characteristic of underwater small targets，comprising the target strength and the multibeam of short range echo highlight of sonar image emulation using the BKY method which used to forecast the large size targets such as submarines. The theory was tested and verified by the experiment on the lake. It can be concluded that the target strength of small targets changes dramatically with the angle variation. It is difficult to detect underwater small targets owing to the target strength minor. The optimization of line shape is important to conceal property. The BKY method can be applied to forecast the echo characteristic of underwater small targets. 

Key words: underwater small target, echo strength, angle and distance spectrum