<p>In recent years, urban agglomerations have gradually become the main spatial entities of China’s regional economic form. With deepening of specialization of urban functions in China, it is significant to explore functional division of urban agglomerations for promoting regional coordinated development and integration. Based on the panel data of 18 urban agglomerations in China from 2007 to 2021, this paper empirically studies the nonlinear influence and mechanisms of functional division of urban agglomerations on regional coordinated development by using the two-way fixed effect model. The results show that: (1) The functional division of urban agglomerations has a nonlinear effect on regional development gap, and the two show a U-shaped relationship. That is, with deepening of division of labor, functional division of urban agglomerations shows a facilitating effect on regional coordinated development, and an obstructing effect after crossing the turning point. (2) The intermediary effect analysis shows that borrowing size and industrial efficiency constitute effective ways for functional division of urban agglomerations to affect regional coordinated development. (3) The intensity of inter-city connectivity and local government intervention can both significantly regulate the curve relationship. Specifically, strong inter-city connectivity makes the U-shaped curve steeper and the inflection point appear later, while excessive local government intervention makes the U-shaped curve flatter and the inflection point appear earlier. </p>