Abstract: In order to understand the influence of reservoir construction on the runoff and sediment discharge variations, relationships between water and sediment parameters and reservoir capacity parameters in the trunk stream and tributaries of the Yangtze River were deeply studied through using the incoming sediment coefficient (ISC), the sediment transport modulus (STM) and the reservoir regulation coefficient in the basin (RCB). Annual sediment discharge in the typical hydrologic stations gradually reduces with increase of the cumulative reservoir capacity in the basin, and the ISC and the STM of the rivers decrease in an exponential form with the RCB, which shows that water storage and sediment trapping of the reservoir is a main influence factor on the runoff and sediment discharge variations. The attenuation laws of the sediment discharge in the trunk stream are some differences from that in tributaries. For the tributaries, the ISC and STM attenuation laws are relatively independent with each other. For the trunk stream, the ISC and STM attenuating ranges in the upper stations are greater than that in the lower stations, and it is near same for the STM attenuation laws in all typical hydrologic stations.