Abstract: Due to the impoundment of the Three Gorges project (TGP), runoff process and sediment conditions in the Yaojian reach of the middle Yangtze River, and the riverbed evolution is also changed correspondingly. Owing to operation adjustment of the TGP, the water and sediment inter-annual characteristics are changed, sediment concentration decreases significantly, and the characteristics of discharge and sediment process within a year are changed. After the impoundment of the TGP, the discharge during storage water period was decreased,and the recession duration after flood was shortened. Based on the measured data in 2002 and 2007 before and after the impoundment of the TGP, the difference between 2002 and 2007 has been analyzed in aspects of the riverbed erosion and deposition, the cross-section changes and the navigation channel conditions. In order to study the influences of the TGP on the navigation channel in the Yaojian reach, water and sediment data, the measured terrain data were collected, water-sediment flux analyzing has been done, and a 2D mathematical model was established and used to calculate the deposition and erosion of the Yaojian reach. The analysis results show that the evolution patterns within a year is characterized by “siltation during flood season and erosion during dry season”. As the sediment concentration decreases during the flood season, siltation in the Yaojian reach decreases compared with that before the impoundment of the TGP. The navigation channel is still under the unfavorable conditions. This is mainly caused by the impoundment of the TGP after the flood season, which changes the flow falling process, decreases the flow discharge, and thus decreases the erosion dynamics.