Abstract: The synergistic development of digital economy and green cities is a key path to realize sustainable regional transformation. Based on the system coupling theory, this paper combines the entropy method, coupling coordination model, geospatial analysis and regression of restricted dependent variables to construct an evaluation system of digital economy and urban green high-quality development of 30 major cities in the downstream area of the Yangtze River Delta for the period of 2013-2022, which systematically evaluates the level of coordination of the two major systems and reveals their spatial heterogeneity and distributional characteristics. The study found that, on the one hand, the synergy level between the digital economy and green city construction within the region has steadily improved, yet there exist obvious spatial disparities, which reflect the asymmetric development of different cities in digital transformation and ecological governance. On the other hand, the region exhibits spatial self-organization characteristics: a high-value agglomeration area with Shanghai as the core and Suzhou and Ningbo as sub-centers has gradually taken shape, demonstrating the leading and radiating role of central cities in the coordination of digital ecology; A multi-factor analysis revealed that technological innovation input, government governance effectiveness, and the development degree of financial markets play a positive role in promoting coordinated development, while scientific and technological expenditures and invention patents show a certain inhibitory effect. This study reveals the dynamic coupling mechanism of digital transformation and green development, enriches the theory of regional sustainable development, and provides a theoretical basis and policy recommendations for regional digital governance and green transformation.