This paper analyzes the ecological water level of a river as the research object based on the improved Tennant method. This method correlates the percentage of the recommended flow in the Tennant method to the annual average flow under different habitat states and the water level guarantee rate, and uses the water level of the guarantee rate corresponding to different habitat states as the ecological water level. The study found that the improved Tennant method applied to rivers can better reflect the natural hydrological situation. The algorithm helps to ensure the healthy development of biological indicators such as river velocity, water surface width, and river depth. The algorithm applied to the river can better reflect the water use characteristics of the river reach. This method is easy to meet the needs of the basin's economic, social and natural development.