Abstract: The middle reaches of the Yangtze River is wide enough that many reaches are braided channels with bars and shoals in the river bed. In those braided channels, the scouring and silting of mid-channel bars and point bars change greatly: some bars decrease, and the others may increase greatly; and simultaneously the thalweg and the main streamline migrate frequently and significantly. After the impoundment of the Three Gorges reservoir, the new features of river bed evolution gradually showed up, and the navigation conditions of those braided channels changed accordingly. This paper takes the Jiayu waterway as an example, which is one of the main navigation-obstructing waterways in the middle reaches of the Yangtze River. On the basis of the existing researches and the recent field observation data, the fluvial processes of slightly curved braided reach are illustrated, and the evolution processes along with the characteristics before and after the impoundment of the Three Gorges reservoir are compared, the factors influencing the river-bed evolution are analyzed, and then the influences of the Three Gorges reservoir are discussed. Finally the river evolution tendency and navigation condition changes are presented. With regard to the Jiayu waterway, the Three Gorges reservoir impoundment changed the cyclic alternating pattern between the single-channel and double-channel of the transition section, and also weakened the relationships between the Wangjiazhou shoal and Fuxing bar: before the impoundment of the reservoir, the shoal shrank and the bar expanded; but after the impoundment of the reservoir, the shoal shrank and the bar also shrank. Under the influences of the Three Gorges reservoir impoundment, the shoals and bars in the middle reaches of the Yangtze River will be further eroded in the long term; as for the Jiayu waterway, the entrance of the left branch will be more flat, the main streamline will meander even more, and the navigation conditions will be more in instable due to the riverbed evolution.