In this paper, the calculation process of ecological hydrodynamic radius method was introduced. Taking the Jialu River, the second tributary of Huaihe River as an example, we calulated the minimum ecological water demand corresponding to different hydrological frequencies of two hydrological stations in Zhongmou and Fugou. Based on the regional climate and geographic features of the study area and demands of fishes on flow velocity within the river basin , the calculation standard of Tennant method was amended. The modified Tennant method was used to verify the calculation results of the minimum ecological water demand of Zhongmou hydrologic station and Fugou hydrologic station. The results showed that the calculation results of minimum ecological water demand of Zhongmou hydrologic station in high flow, normal flow and low flow year and Fugou hydrologic station in high flow and normal flow year are reasonable, but the minimum ecological water demands of Fugou hydrologic station in low flow year can't meet minimum value set in Tennant Approach in majority months, which can be replaced by results calculated by Tennant Approach. This approach gives more consideration on river hydrology and hydraulics features and demands of habitats for aquatic organism in river ecological system , which has more ecological significance.