Unidirectionally-migrational channel-levee system well develops in the deep area of Baiyun of the Pearl River Mouth Basin, the South China Sea and in Lower Congo Basin, West Africa. The channel shows obviously migrating characteristic, which results from interaction between gravity flow and contour current. Furthermore, migrating direction of channel corresponds to the direction of contour current. It is likely to be controlled by relatively energy of gravity flow and contour current, sediment supply, fluctuated sea-level, climate, morphology, Coriolis force, width of shelf and so on.