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.