The nearshore water area is a very important part of maritime safety and application water area. Due to the complexity of sound propagation, and the influence of terrain, geology, tidal range and experiment’s difficulty, there has few researches in this area. Based on an existing engineering works, this article attempts to give some related calculations of the bistatic backscattered acoustic strength received and launched by a high frequency sonar in the extremely shallow water area with the depth less than 10 meters, and followed by in situ experiments test. It shows that the calculated results are in good agreement with the experimental tests. This work is a preliminary attempt in the study of extremely shallow water areas, and will provide a certain reference for the later sonar work in extremely shallow water areas.