Structural units of a deepwater depositional system are canyons, channels or channel complexes, levee-overbank, lobes and mass-transport deposits. By means of the seismic reflection data from different areas in Rakhine Basin, Bay of Bengal, the typical seismic response characteristics and developing locations of different structural units are analyzed to establish a evolution model of the deepwater structural units from the shelf through the slope and the basin. It is indicated that a deepwater sediment system evolves upwards from the base as follows:(1) mass-transport deposits and a large-scaled thick lobe at the base, (2) an overlying channel complex at the lower part, (3) a channel-levee complex or a small-scaled lobe in the middle-upper part, and (4) capping thin abysmal sea mudstone at the top. In lateral, the deepwater sediment system is composed of shelf/upper slope canyon, upper slope erosive channel, lower slope erosive-depositional channel, depositional channel and basin-floor lobes from the shelf to the basin.