Abstract: For active detection of underwater target in deep sea environment, the model of normal mode coupled boundary element method is established. In this paper, the acoustic propagation characteristics in deep sea under Munk sound speed profile are simulated firstly, and then based on the propagation characteristics the scattering echo strengths varied with horizontal distances and vertical depths are calculated when the source located at different depths. The simulation results show that the target scattering echo strength near the convergence zone is large due to the influence of complete sound channel when the source located at the depth of 100 m (near the sea surface) or 1 400 m (channel axis). and the target scattering echo strength is large in the middle and short ranges (less than 40 km) due to the influence of direct wave and surface reflected wave when the source located at the depth of 4 900 m (near the sea seabed). The results also show that the larger detection range may be achieved when the receiving hydrophones located at the depth deeper than critical depth.