Abstract: The method of imaging the submarine sediment layers'echo data is to study the geologic structure with the information simulated by a profiler and received by hydrophone streamers at the sea surface.In this paper,acoustic wave equation,which describes the acoustic waves propagation,is used to backward extrapolate the observed echo wavefield.When the medium is homogeneous or horizontal layered,time imaging method is valid.But when the structure is complicated,the diffraction term is collapsed and the thin lens'term caused by the lateral velocity variations is time shifted as the wavefield is downward continued.Such a method,called depth imaging,can provide a good image to determine the sea-bed sediment layers.