The lower section of the south branch, where many active shoals distribute, is the reach with the most frequent and most complicated river regime evolvement in the Yangtze estuary. The paper presents the process and outcome of the 2D numerical simulation about the hydrodynamic condition and the riverbed’s evolvement under the natural condition and the condition of implementing Biandansha shoal protection project, which may serve as reference for the research of south-branch’s river regime evolvement and controlling project.