Yichang low-water level was an important parameter connected with the operation of Gezhouba ship lock. It had kept stable while a huge amount of sediment erosion had been caused during TGP’s (Three Gorges Project) initial impoundment period, and its reason wasn’t very clear now. Analysis of the riverbed boundary condition changes was presented in this paper, and it showed that the stable planmetric figure, function of the bottle-neck reach, non-uniformity of the bed erosion, increase of the bed resistance were the main reasons for the stability of Yichang low-water level. Because of the function of the bottle-neck reach, there would be no big fall of low-water level at Yichang station.
