Abstract: The flows suggested by Tennant method cannot be used to solve the ecological water demand problem of the rivers without flow data, this paper proposes an improved ecological water level calculation method based on Tennant. In this method, water level guarantee rate is connected to the percentage of the discharges proposed by Tennant under different habitat status in the average annual flow, and the water levels of various guarantee rates corresponding to different habitat status are determined as ecological water levels. Taking the ecological water level calculation of the Huaihe River Sea-entering Channel as an example, 19 hydrology stations with long flow data series on the main stem and tributaries of the Huaihe River Basin are selected as reference stations. The hydrological guarantee rates corresponding to the flow thresholds recommended in Tennant are estimated by P-Ⅲ curve, and the results of various stations are analyzed comprehensively to get the hydrological guarantee rates corresponding to the Tennant ecological flow, which are applied to the calculation of the ecological water level in the estuary channel without flow data. The results show that the hydrological guarantee rates for the poorest and best conditions in the Huaihe River Basin are 90.2% and 27.0%~41.6% respectively. The water level of the Huaifu Control floodgate and the Dongshagang floodgate should be maintained at 1.26-1.83m and 1.08-1.72m in order to guarantee the ecological health of the Huaihe River Sea-entering Channel. This method provides a new insight for ecological water level calculation in rivers without flow data.