The rationality of the population distribution of urban agglomerations is related to the high-quality development of urban agglomerations. Aiming at maximizing the economic benefits of urban agglomerations, this paper deduces the formula for the Structure Rationality Index (E-Zipf) of population distribution. It uses the panel data of 19 major urban agglomerations in China from 2010 to 2020 and adopts the systematic GMM method to calculate E-Zipf. The results show that the E-Zipf index of urban agglomerations in China is 1.33, which is higher than 1. Taking 1.33 as the standard, compared to the traditional standard of 1, the population distribution of 6 urban agglomerations is under-agglomeration rather than over-agglomeration. The results of rational classification show that the population distribution of 6 urban agglomerations, 5 urban agglomerations, and 8 urban agglomerations is reasonable, over-agglomerated, and under-agglomerated, respectively. Over-agglomerated urban areas need to disperse the population of the central city and appropriately develop the peripheral cities, while under-agglomerated areas need to continue to concentrate population in their core cities.

Population spatial agglomeration is the basis for the economic growth of urban agglomerations in China. A dynamic panel regression model is established on the basis of the theoretical derivation of the relationship between population spatial agglomeration and economic growth in urban agglomerations. The study has three major findings. (1) The spatial concentration of population in urban agglomerations in China has a significant impact on the economic growth of urban agglomerations. (2) The effect of population agglomeration on economic growth in urban agglomerations is a non-linear “inverted U-shaped” relationship. At the initial stage of population agglomeration, the population agglomeration to the core cities within urban agglomerations is conducive to improving the economic efficiency of urban agglomerations, and after the population agglomeration reaches a certain level, the economic efficiency will be weakened. (3) Industrial structure optimization and technological progress are useful for the economic growth of urban agglomerations. Capitalizing on the urban agglomeration dividend, it is important to reduce the negative externalities of excessive spatial concentration of population in urban agglomerations, thus promoting high-quality development of urban agglomerations.