This article researches the hydrodynamic condition in channel siltation at the mouth bars of the Yangtze estuary.From the research results,some perceptions are as follows:1)In the mouth bars,flow dynamic is the main power of erosion in the deep-water channel of north passage,and the erosion power generally enhances in the channel,after the 12.5 m channel at the Yangtze estuary being through.2)The correlation between the change of runoff and the siltation in the deepwater channel of north passage is not distinct.3)At the mouth bars of the Yangtze estuary,water flow is a kind of relatively stable power with periodic change;there is no obvious difference between flood season and dry season.4)Under the natural condition,the riverbed at the mouth bars of the Yangtze estuary is in a dynamic equilibrium which is resulted from the flow dynamic and wave dynamic.When it is only under the action of flow dynamic,the riverbed at the mouth bars of the Yangtze estuary is not in an equilibrium state any more,and the scouring depth tends to further develop in the main channel.