Abstract: This paper analyzes the erosion efficiency of floods in the lower Yellow River during the storage periods of the Sanmenxia reservoir and the Xiaolangdi reservoir The results indicate that,when the discharge is less than 4 000 m³/s,the erosion efficiency of the total sediment in the downstream of the dam increases with the increasing of average flood discharge, while it maintains a constant value when the discharge is greater than 4000 m³/s. By investigating the erosion efficiency through the group sediment,we find that the decrease of the erosion efficiency of the fine sediment load is higher than the in creae of the erosion efficiency of the coarse one,which may be the crucial reason why the erosion efficiency of the total sediment load does not increase with the increase of the average flood discharge any more when the discharge is greater than 4000m³/s. The supply of the fine sediment load from the riverbed is the major factor affecting the erosion efficiencies of the total sediment load. It is suggested that the average flood discharge during the storage periods of the Xiaolangdi reservoir should be controlled at about 4000 m³/s to obtain the highest erosion efficiency. We can make good use of the limited water resources and improve the drainage capacity of the channel in the Lower Yellow River.