Abstract: The stageⅠregulation work of deep water channel of the Yangtze River estuary and the topographic change of the lower-section of the Jiuduan Sandbank(JS)after regulation are simply described. The non-linear three2dimensional numerical model under the σcoordinate system is applied,which is verified by the field observations. According to the measured topographic change of the lower-section of the JS after and before the stageⅠregulation work(from May 1997 to March 2000),the tidal flow discharge,the Euler's residual flow and the current velocity characteristics in the middle and lower sections of the North Channel are simulated by using the model in order to interpret the hydrodynamic mechanics of sediment movement and topographic change.