Tributary inflow will result in localized lateral flow in the main steam as well as significant water level fluctuations.Changes in flow conditions can adversely affect the safe navigation of the canal.Under natural conditions，lateral flow velocities at tributary confluences in localized areas exceed the minimum requirements of the navigational criteria，which seriously affect the safe navigation of the waterway.The optimization of the exceeded section of the river is required.In view of impact of flood discharge tributaries on navigable flow conditions in canals during flood season，the renormalization group (RNG) k-ε turbulence model is adopted to carry out the three-dimensional fine numerical simulations，and navigational conditions in the confluence area under different combinations of flood flows are studied.The results show that although the widening of the channel can effectively improve the flow conditions in the confluence area，the lateral flow velocities in some areas still exceed the standard under the original design scheme.The measures are adopted for the optimized scheme，such as moving down the connecting section，setting up water diversion retaining walls，and widening the river way and etc.When the optimized scheme is applied，the overall navigational conditions in the confluence area are satisfactory，and the flow and water level conditions can meet the requirements for safe navigation of ships.