The article analyses the flow and sediment characteristics in tongzhou beach,channel depth conditions and channel changes.From the river regime change and the change of riverbed erosion and deposition beach trough,the article analyses the reason of deepwater channel obstruction in Tongzhou reach.The research shows that because of the channel widening，bottomland instability,flow separation and separation of ebb and flow tide direction in Tongzhou beach,it leads to unstable regime instability and beach trough.First of all,channel widening,bottomland shunt lead to flow concentration and deep channel silting-up in transition section leads to impeding navigation.Secondly,channel widening,mainstream swing,point bar silting up and char movement leads to the shortage of channel depth.Besides that,bar-beach transition,main channel variation accordingly,and beach-trough instability lead to navigation channel instability.Keeping the activity bottomland in Tongzhou sand beach stable is the key to river regime stability and waterway regulation.