The discrimination and recognition of underwater targets has been the focus of active sonar detection. The structural characteristics of the target echo arrival in the bottom bounce area are analyzed when the target depth is greater than the transmit-receive depth. A 9-path arrival structure model is established. The relationship between the time delay of the bottom reflected/ surface – bottom reflected path and the target depth is analyzed. A method is proposed to estimate the time delay by searching for target arrival structure in bottom bounce area, and to estimate the target depth by using the relationship between the time delay and the target depth. The algorithm was verified based on explosion sound source data. The estimated depth of the underwater target obtained by a single hydrophone is in good agreement with the real target depth. The depth estimation of 20 targets within 25.6km was carried out, among which the depth estimation error of 17 batches was less than 10m, and the average depth estimation error of 20 batches was about 7m.