Ecological flow of rivers and lakes is a basic index to maintain the ecological function of rivers and lakes and control the intensity of water resources development and utilization. The control of river ecological flow is related to the overall situation of ecological civilization construction and plays an important role. The water conservancy and hydropower projects on rivers and lakes play an important role in regulating the flow of rivers and lakes. At present, the ecological flow verification of the existing water conservancy and hydropower projects is underway. The accessibility and coordination analysis of the ecological flow target of the existing water conservancy and hydropower projects is a difficult problem in the current work. In this paper, a method for determining the accessibility of ecological flow targets of existing water conservancy and hydropower projects in the process of ecological flow verification in data-deficient areas is proposed. The Dadan River Basin in Dali City, Yunnan Province is taken as an example to calculate and compare with the results of fine model for water resources allocation. The results show that this method can be used to judge the accessibility of the ecological flow target approval of the built water conservancy and hydropower projects in the data-deficient areas, and provide a reference for the accessibility and coordination analysis of the ecological flow of the built water conservancy and hydropower projects in the approval work.