Based on hydrological observation data in the North Passage of the Yangtze River,we apply three-dimensional numerical model to simulate saline wedge,water current,and sediment transportation.The results show that obvious differences exist between the sediment of surface and bottom layer,and the distribution of sediment is uneven vertically.Sediment is more likely to concentrate in the middle North Passage,due to saline wedge.At the same time,the distance from the upper North Passage to open seas is so long,that sediment could hardly be transported out of the North Passage during an ebb-tidal duration,which greatly increases the possibility for the sediment to transport cross the waterway.Especially,high-concentration sediment often silts in waterway when current changes direction with low velocity and long duration in the middle and lower North Passage.Even after the sediment is transported out of the North Passage,rotary current may carry part of the sediment back to the North Passage through Jiuduansha wetland and south jetty.This transport pattern happens repeatedly,which contributes to high sediment concentration in the North Passage.