According to the river basin planning of the Ganjiang river,the Xin’gan navigation electricity hinge will be proposed at about 1.5 km upstream from Sanhu town.It must be predicted that the change tendency of river bed and water levels downstream hub after completion of the project.The 1-D flow and sediment mathematical model are established from Sanhu town to Nanchang for 118 km long reach.The deformation of river bed and the declining water levels are computed by numerical model after completion of the project.The conclusion shows that under the current river status,the river bed will reach a equilibrium state by scouring and deposition for 6～7 hydrological years;the maximum scour depth of the river bed will be 1.76 m and the maximum value of the declining water levels will be 1.56 m after the self-adjustment of river bed about 10 hydrological years.The change of waterway condition downstream of the Xin’gan hub is analyzed.