The navigational condition of Tuqiao waterway has deteriorated since 1998,but the navigation-obstructing characteristics have varied with time.Therefore,this dissertation attempt to delve into the mutation of the navigation-obstructing characteristics.Firstly,it draws on data from the topography and hydrology of Tuqiao as well as the date of water and sediment from Datong hydrological station during 1955 to 2014.Secondly,by using the ordered cluster method it analyzes the changes of sediment discharge of Datong hydrological station,and the reasons of the variations of navigation-obstructing characteristics.The results show that the navigation-obstructing characteristics have changed from the problems of section shape and silty-sand to the declining split ratio of the left branch.The main reason is the changes in the water and sediment process of Datong hydrological station after the impoundment of Three Gorges Reservoir.The new process of water and sediment is detrimental to the maintenance/stabilization in the flow diversion ratio of the left branch,which specially causes a significant decrease in the flow diversion ratio after the operation of 175 m water impoundment scheme,and has become the main reason of the worsening navigational condition.