Can Urban Agglomeration Construction Promote the Synergy of Digitalization and Greening?

As critical spatial carriers for concentrating factor resources related to digitalization and greening, urban agglomerations provide key platforms for advancing the synergistic development of these two domains. Drawing on a city-level panel covering 280 prefecture-level cities in China over 2003–2023, this study applies a time-varying difference-in-differences (DID) framework to evaluate the influence of urban agglomeration construction on digital-green synergy and to clarify the mechanisms through which this influence occurs. The empirical evidence shows that urban agglomeration construction exerts a significant positive impact on digital-green synergy. The effect is more evident among cities in the small and medium-sized categories, cities with relatively weak initial synergy, regions characterized by stronger government cooperation awareness, and cities located closer to central cities. It is also more evident in relatively underdeveloped regions. Mechanism analysis shows that urban agglomeration construction improves digital-green synergy mainly by reinforcing industrial collaboration, which strengthens inter-city specialization and complementary advantages. Moreover, alleviating market segmentation and accelerating factor flows further increases the positive effect of urban agglomeration construction on digital-green synergy. These findings offer empirical evidence and policy implications for improving urban agglomeration development strategies and promoting urban digital-green synergy.