The spatial structure reflects the hierarchical structure, functional structure, and community form between cities in the urban agglomeration, representing the expansion model and development characteristics of the urban agglomeration within a certain time range. In this study, the urban agglomeration in the middle reaches of the Yangtze River (UAMRYR), which is the first approved national urban agglomeration in China, is selected as the research object. The land use / land cover datasets, Landsat images, and urban population data were used in this study to analyze the evolution process and characteristics of the UAMRYR during 1990-2019 at the macro and micro levels. The research methodology includes the development of the spatial database, construction of the grid system, calculation of the urban expansion degree, and building of the expansion rose map. Based on the characteristics and the rules of historical development, a scenario analysis is processed on the development situation for 2020 and 2030. The main conclusions are as follows: (1) From 1990 to 2019, the spatial structure of the UAMRYR has transitioned from "three centers" into "single core, double centers, and multi- clusters", and then into "double cores, multi-centers, and multi-clusters". The "double cores" of the Wuhan metropolitan area and the Changsha-Zhuzhou-Xiangtan urban agglomeration has developed into giant cores and will continue to expand during 2020-2030, becoming superlarge cores with built-up areas of about 2000 km2 and 1500 km2, respectively. Nanchang is relatively small and would remain as the regional development center radiating the Jiangxi Province. Seven development sub-centers have been formed, namely Xiangyang, Yichang, Jingzhou, Changde, Hengyang, Jiujiang, and Shangrao, and are expected to increase further in the future. (2) In the development process, four main axes of the Yangtze River, Wuhan to Changsha, Wuhan to Nanchang, Nanchang to Changsha, and several secondary axes have been formed. However, due to the lack of strong border hub and bridgehead city, the driving force of the axes on the urban agglomeration needs to be further improved. (3) There are several development problems in the area. The polarization effects of cores in the Wuhan metropolitan area and the Changsha-Zhuzhou-Xiangtan urban agglomeration are extremely strong and continue to present a development trend. Jiangxi Province lacks a strong core, thus various environmental problems emerged due to the over-concentration of urban built-up areas. These places are urgently adjusted in order to control the speed of expansion, cultivate new regional centers, and strengthen the axis function.