If the dam-front water level of the open junction is adopted in the design of the upstream lowest water level of the medium & low-head canalized junction,the following problems easily arise:the lower bottom elevations of the upstream approach channel and threshold on ship-lock not only enlarge the wall section and increase the cost,but also easily lead to siltation;the flow pattern of the upstream and downstream channel entrance area is poor,so it is difficult to satisfy the requirements of ships’ safety entry and exit.Based on several engineering examples and according to the results of integral hydraulic model test,this article analyzes the rationality of using the dead water level of the junction as the upstream design lowest navigable stage through hydrological calculation and comparison of the navigation flow conditions,the navigation guarantee rate and the project investment.At the same time,combining with the backwater analysis of different operation modes of the junction,it is concluded that the water level connection between the upstream and downstream cascade of canalized river can meet the requirements when the junction run with dead water level and it is feasible to use the dead water level of the junction as the upstream design lowest navigable stage.