Abstract: Fill-scour threshold is often related with specific combination of sediment load and stream flow, and determining of this combination may provide important reference to the operation of Xiaolangdi Reservoir. Based on annual hydro-metric data and using statistical method, a study has been made to determine the fill-scour thresholds of the lower Yellow River, for two periods separately, namely, the period with channel shrinkage from 1986 to 1999 and the period from 1950 to 1985 without channel shrinkage. A number of fill-scour thresholds have been obtained, which show that the fill-scour thresholds related with annual suspended load, with annual mean sediment concentration, with annual concentration of "coarse" sediment and with the ratio of annual sediment concentration to water discharge (known as incoming sediment coefficient) all decreased from the non-shrinkage period to the shrinkage period. This means that in the latter period sedimentation might occur even if the annual mean sediment concentration and the incoming sediment coefficient is at a lower level than that in the former period, and thus, flood protection in the lower Yellow River would face higher pressure.