Longmen waterway is the key impeding navigation channel due to its shallow,chaos and rapids flow.Based on recent field investigation data,the flow-sediment property,variation of depth contour,thalweg and typical cross sections were studied,navigation obstruction was analyzed.Results show in 2007—2015,plane form of Longmen waterway was steady;shoal lines changed a little,river bed scoured and silt alternatively.Affected by upstream reservoir,decreased incoming sediment led to slight erosion in low channel.Large difference between flood and dry river width resulted in siltation in bend convex bank,in middle and low water flow,rapids flow appeared neighbouring Dahe spur dike,and chaos flow formed nearby the head of Longmen rock spur.