The channel-shoal system in Qinzhou bay consists of east, middle, west three major tidal channels and interpolating sand shoals (ridges). Numerical modeling of the morphodynamics of the channel-shoal system is performed using 3D unstructured grid, finite volume, paralleled computation FVCOM. Erosions occur within channels and depositions occur on shoals and at the end of channels, reflecting that tidal flow is really the dominant force to maintain and modify the channel-shoal system; two large-scale dredgings at the east channel during Sep. 2000 and Dec. 2012, and Feb. 2004 and Dec. 2008 respectively have caused the present sea bed erosion & deposition adjustment in the whole Qinzhou bay, the magnitudes of which are large initially but decreasing steadily;this adjustment process will last over 100 years if no further coastal engineering project is conducted and other presumed conditions are maintained. The morphological adjustments caused by various constructed and planned engineering projects might reinforce each other. This needs further comprehensive modeling study.