The influence of high-speed railway on urban green technology innovation represents a pivotal area of study within the broader research on the impact of high-speed railway on regional innovation. To investigate the effect of high-speed railway on the“dual enhancement of quantity and quality”in urban green technology innovation, a multi-period Difference-inDifferences (DID) model was established. This model utilises panel data from 41 cities within the Yangtze River Delta urban agglomeration spanning the years 2004 to 2019 to explore how the high-speed railway opening influences urban green technology innovation. The findings reveal that the introduction of high-speed railway significantly promotes the“dual enhancement of quantity and quality”in green technology innovation across the Yangtze River Delta cities. Mechanism analysis further indicates that high-speed railway impacts urban green technology innovation by bolstering economic agglomeration and venture capital investment. Additionally, the effects of high-speed railway opening exhibit heterogeneity in terms of city size and regional characteristics, with notable impacts observed in both large cities and small to medium-sized cities. Specifically, the influence of high-speed railway is more pronounced in Jiangsu Province compared to Zhejiang and Anhui Provinces. This study systematically elucidates the relationship between the high-speed railway opening and the“dual enhancement of quantity and quality”in urban green technology innovation within the Yangtze River Delta region. The conclusions remain robust following rigorous stability tests.