The potential changes are occurring in the Earth's water cycle due to climate change and human activities, which cause water supply system mainly affected by hydrological processes are extremely complex and variable. Water resources management based on water demand has been not an accurate reflection to the regional water resources status. It needs us develop water resources management from the perspective of water cycle. This study introduces the basic theory and method of water resources management based on evapotranspiration (ET) control, and put forward the ET-based model on county-territory scale and its calculation method. The ET-based model is different from the traditional method, origins from regional water cycle process and stresses the natural attributes of water resources. In addition, this study considers Luannan County with over-pumping groundwater and further discusses the case study about water resource allocation based on ET. The research shows the ET-based model chooses ET control as the means, cutting ET as the goal, physical drive processes of water resources as theoretical basis, and takes into account many practical problems related with county development such as the industrial development, planting structure, water-saving potential and excessive exploitation of water resources. The treatment can make the planning scheme from the model is accord with the actuality of regional development and give controlling the over-pumping exploitation of water resources more maneuverable.