Recognizing the core commonalities and inherent laws of population development of world-class city clusters is a necessary path to understanding the incubation mechanism of urban agglomerations. Based on the collection of long-term historical population data and regional spatial planning data, we employ Lorentz curve, spatial Gini coefficient and other methods, taking the overall urban agglomeration and central city population growth as observation indicators, to compare the population of six world-class city clusters, and changes in scale, agglomeration characteristics and evolutionary process. The population of the six world-class city clusters has shown a common “life-cycle” development process, which is manifested in the continuous strengthening of population resource advantages, the hierarchical differentiation of population spatial structure, the prominent siphoning role of the central city, and the gradual narrowing of the gap between the total population of the primary city and the central city. In the process of expansion and contraction of different types of cities, urban agglomerations generally experience a transformation from single-core polarization in the first city to multi-point aggregation in the central city, the continuous strengthening of the urban agglomeration circle pattern, and the dual stability of the urban agglomeration order pattern. “Symbiotic” rather than “zero-sum game” inter-city agglomeration of population has become the main driving factor for the population development of world-class city clusters.

Based on the evolution of the megalopolis theories and the analyses of population census and statistical yearbook data，this study explores the issues of coordination development of Megalopolis’s population．Based on a clear distinction between the concept of core area and core city，and using methods of spatial autocorrelation and industrial structure deviation analyses for comparing the spatial scale，space structure of population and spatial coordination of industry between Northeast megalopolis in USA and Beijing-Tianjin-Hebei megalopolis in China，this study shows that for a typical megalopolis，its incubation process presents a significant stage development pattern．The population proportion of its core city rises at the beginning，and then declines．The spatial distribution of population shows a changing trend from single pole to multi growth poles．The spatial structure of population has both characteristics of aggregation and dispersion．The adjustment of industrial structure in core region has major implications to the coordination development within Megalopolis．