AbstractThis study combines the Defense Meteorological Satellite Program’s Operational Linescan System (DMSP/OLS) nighttime light data with the Suomi National Polar-Orbiting Partnership satellite visible infrared imaging radiometer suite (NPP/VIIRS) nighttime light data, to research 21 urban agglomerations in China from 1995 to 2015. The expansion is described by analyzing the changes in the area, expansion intensity, and relative development speed of different urban agglomerations. First, nighttime light image from different sensors are mutually corrected according to eight partitions. Then, the built-up areas are extracted. Lastly, the brightness is calculated to analyze the distribution and characteristics of urban agglomeration. This paper reveals the following results: (1) Urban expansion in the northern and western regions is lagging that of the eastern and southern regions. The eastern region shows the most obvious change for all regions; (2) The Yangtze River Delta, the Pearl River Delta, and Beijing–Tianjin–Hebei have changed the most. Central Guizhou, Chengyu, and Poyang Lake Ring are growing the fastest. Jinzhong, Harbin-Daqing-Changchun, and the Pearl River Delta have the slowest growth intensity; (3) The internal characteristics of urban agglomerations are measured by internal development differences and relative development rates. Moreover, they can be divided into “single-core,” “dual-core,” “group,” or “striped” development modes.