Abstract: Since green development can effectively alleviate ecological and environmental problems, it can promote higher quality integrated development of the Yangtze River Delta Urban Agglomerations. On the basis of sorting theories and mechanisms of green development, this paper develops an indicator evaluation system of green development with six dimensions as scientific and technological innovation, economic growth, resource utilization, environmental governance, environmental quality, and green life, and measures and analyzes the spatial-temporal evolutionary characteristics and future change trends of green development level in Yangtze River Delta Urban Agglomerations from 2006 to 2019 by using Entropy Method, Kernel Density Estimation, and BP Time Series Forecast Model. Research results show that: during the study period: (1) the green development level of the Yangtze River Delta urban agglomerations showed a fluctuating increase in general, and the green development level of some cities declined in 2008-2009 and 2011-2013 due to financial crisis and industrial transfer. （2) green development level between cities had gradually prominent discrepancies, with polarization and a tendency to tripolarization, meanwhile the spatial distribution is uneven. (3) during the “14th Five-Year Plan” period, the green development level will increase further, and it will be improved in the northern and southern regions, but still remain at a low level in the western region. (4) the grade transfer of green development level occurs between adjacent grades, with no “grade skipping” phenomenon and indicating that there is a “bottleneck” of the Yangtze River Delta urban agglomerations. Finally, based on the regional characteristics of the Yangtze River Delta urban agglomerations, this paper proposes corresponding suggestions for green development.