The sedimentation impacts of incoming water and sediment from the six observation stations in the middle reaches of the Yellow River on Sanmenxia reservoir and its downstream area are studied by using the sediment discharge balance method. The downstream sedimentation index induced by incoming sediment from the middle reaches of the Yellow River

the area rich in sediment and coarse sand

and the source area dominated by coarse sand are analyzed by using profile method. Results show that incoming sediment from Longmen station has the greatest contribution to sedimentation in the lower reaches; incoming sediment from Huaxian County

Hejin

and Zhuangtou stations has smaller contribution; and incoming water and sediment from H eishiguan and Wuzhi stations are favor of downstream scour. Analysis by profile method indicates that the amounts of sedimentation in Sanmenxia reservoir and its downstream area are 0. 25

0. 257

and 0. 329 hundred million tons for one hundred million tons of sediment from the middle reaches of the Yellow River

the area rich in sediment and coarse sand

and the source area dominated by coarse sand

respectively. The coarser sediment

the greater contribution to downstream sedimentation is.