The seagoing ship channel in Baimaosha reach of the southern branch of the Yangtze River has always been changed since its opening in 1965.Analyses show that channel instability relates to the instability of river regime,beaches and grooves.Navigable channel will not be stable without stable river regime.The rise and fall of branch channels and deep trough changes both lead to channel changes,and channel instability also relates to the upstream river regime’s instability of Tongzhoushal reach and back flow of water and sediment from the northern branch of the Yangtze estuary.With the relatively stable upstream river regime,Xuliujing and Changjiang mainstream tends to be relatively stable at the southern side,and Baimaosha southern waterway will be the seagoing ship channel stablely.Considering the changing trends of river regime and channel depth conditions,this paper selects Baimaosha southern waterway for the deepwater channel.