With the building-up of the upstream hydro-junctions, the coming water & sediment conditions and the riverbed of Yichang to Datong River reach changed greatly, and the navigation datum and lowest water level appeared different degree of deviation. So it is necessary to study the adaptability and adjustment of the navigation datum. Based on the real-measured data of the discharge and water level since the use of the current navigation datum, the article analyzes variation characteristics, reasons and trend for the lowest water level, and realizes that the navigation datum of Yichang to Zhicheng River reach adapts well, but that of Zhicheng to Datong River reach is poor. Based on these, the article discusses the train of thought on the adjustment of the navigation datum.