Abstract: This study uses the range of variability approach (RVA) to analyze the data series of average daily runoff and sediment concentration at the Toudaoguai hydrological station on the Yellow River mainstream, focusing on quantitative changes in daily runoff and sediment load caused by the joint operation of Longyangxia and Liujiaxia reservoirs. Changes in the characteristics of synchronous frequencies of monthly runoff and sediment concentration are also evaluated using two-dimensional joint distributions based on the Copula function. Results show that in the period of 1962-2010, runoff and sediment concentration were decreased to a medium extent with the change in runoff relatively more significant. And both were more affected in flood season and annual extreme conditions. In the open flow period of the river, synchronous frequencies of monthly runoff and sediment were increased and were greater than asynchronous ones. This study would help water-sediment joint operation for improving comprehensive benefits of reservoirs.