In view of an exploration of the network structure characteristics of urban agglomerations, based on the passenger transport data of urban agglomerations in 2010 and 2020, a research has been conducted on the topological structure of the spatial network of the three coastal urban agglomerations by using the social network analysis, followed by an analysis of its internal economic effect. Meanwhile, an investigation has been made of the hierarchical structure of urban agglomerations by using the natural fracture method. The results show that there is the largest spatial correlation network density of urban agglomeration in the Pearl River Delta with a stronger links between cities, to be followed by Beijing-Tianjin-Hebei urban agglomeration, while the Yangtze River Delta urban agglomeration is rather weak, due to the fact that the Yangtze River Delta urban agglomeration spans a wide area with an uneven links between various provinces. The spatial network of Beijing-Tianjin-Hebei urban agglomeration is characterized with a typical primary and secondary structure, the Yangtze River Delta urban agglomeration a typical polycentric structure, while the Pearl River Delta urban agglomeration a panic-deep dual-core structure, with the distance between cities, factor diffusion and agglomeration, industrial structure and economic globalization exerting a significant impact on the division of agglomeration subgroups.