In recent years, although the sediment yield from source areas ranged from Hekouzhen to Longmen in flood seasons is less than before, but the mean sediment concentration of floods is continuously increased.The causes of such a fact are as follows.(1) Exploitage of water resources in clear water region takes precedence over all the other areas in the upper Yellow River.(2) Those tributaries in primary sediment yield areas of the middle Yellow River almost all carry heavy sediment load; (3) The harness and conservation of these in tributaries basins have no ohvious effect on sediment yield reduction.Especially the total runoff passing through the Hekeuzhen Station in flood season will be reduced greatly once again when the Longyangxia project.a large reservoir with long-term regulating capacity, will put into operation.or even the river flow will he cutoff for a long time during the irrigation sea-son.As a result, the basic flow in lower Yellow River may he reduced and the sediment concentration may be increased.Thus the occurrence opportunity for hyper-concentrated flood may he increased.The lower Yellow River will face an unfavourable situation with larger amount of sediment and less water in flood seasons.Therefore the problem how to remould the wide-shallow river channel of the lower Yellow River and fully utilize the narrow-deep river channel for transporting hyper-concentrated flow into the sea should he positively researched.