Hydrological indicators with ecological meaning including flow, frequency, timing, duration, rate of change are selected to do the analysis. The approach is that, simplifying multi-characteristic values into a single integrated indicator, which describing the suitability degree of the aquatic organisms to the river flow. As a case study, flow data in the recent 50 years at Yichang, Hankou and Datong hydrological stations in the middle and lower reach of Yangtze River are selected to analyze the suitability degree of Chinese Sturgeon and Four Major Chinese Carps to the flow of Yangtze River. The results show that, it′s feasible to choose the integrated indicator to reflect the suitability degree of the aquatic organisms to river flow, which indicates the deviation degree of the river flow from the suitable ecological flow. It is significantly important to guarantee the suitable river flow process for the normal life of organisms in the river.