The Yangtze Estuary 12.5 m Deep-draft Channel has been available for navigation since March 2010.Despite its enormous economic and social contribution,the problem of back silting is outstanding.The siltation is mainly occurred in the North Passage which crosses the maximum turbidity zone of the Estuary and highly centralized by time and space.The channel middle part is the peak siltation segment.Meanwhile,most of the siltation appears in flood season from June to November.Based on the hydrological data along the North Passage,it is analyzed that the spatial and temporal distribution and transport laws of tidal flow,sediment and salinity in the North Passage.It is revealed that the main reasons of siltation concentration in the channel middle part during flood season,and the sediment transport physical process during flood and ebb tide cycle is put forward.