Nanchang river is located on the upstream of the Ganjiang river segment (Nanchang to Hukou).Recently，affected by human factors，in great changes of river bed，water flow characteristics，the river bed and flow characteristics have changed a lot，thus the design water level shall be changed accordingly.For the reasonable design water level，according to the situation of recent riverbed evolution and flow conditions of Waizhou station，we carry out a comparative analysis with synthetic duration method，frequency-duration method，as well as stage-discharge relation.The result shows that the design highest navigable level changes a little recently and thus shall be determined with the frequency-duration method，the design lowest navigable level has been lowering obviously and shall be determined with the stage-discharge method.