Abstract: Dividing the boundary of urban agglomerations is not only a theory problem, but also a practice problem in the course of planning and construction of urban agglomerations. In this paper, firstly, the improved gravity model by combining the method of main composition analysis and the comprehensive strength of cities is used to primarily divide the boundary of Chang-zhu-tan urban agglomeration. The end and the limitations of using gravity model to divide the boundary of urban agglomerations are analyzed and discussed, too. some errors between the theory end and the real status are easily caused because of the limitations of gravity model itself, for example, the location of gravity breaking point is easily disturbed by the city administrative area shapes, etc. So, some else methods must be used to rectify the boundary of Chang-zhu-tan urban agglomerations. Taken into account production elements flow are the most base feature of urban agglomerations system, the analyses of production elements flow between the different cities are used as the method to further divide the boundary of Chang-zhu-tan urban agglomeration, including the information flows and the passengers flows about the different cities in Hunan Province are fully analyzed. Finally, the current boundary of Chang-zhu-tan urban agglomeration is divided by synthesizing the two methods, and the neighborhood feature of urban agglomerations and the acting force of governments to urban agglomerations also are thought over to predict the future boundary of Chang-zhu-tan urban agglomeration.