Government data openness will have a significant impact on promoting green economic innovation activities. Investigating the mechanism of how government data openness affects urban green innovation efficiency is of crucial significance for accurately understanding their relationship, promoting efficiency in facilitating green economic development. Using panel data from 286 prefecture-level cities from 2011 to 2021, a multi-period double-difference model was employed to explore the impact of government data openness on urban green innovation efficiency. Government data openness effectively enhances urban green innovation efficiency. The results show that open government data can effectively enhance the efficiency of urban green innovation, and the impact is mainly realized through three paths: promoting talent concentration, stimulating innovation and entrepreneurship, and optimizing the regulatory environment. Heterogeneity analysis shows that the effect of open government data on urban green innovation efficiency is stronger in cities in central and western China, with high public concern for environmental protection and high levels of network infrastructure. Extended research finds that open government data can realize the "quantitative and qualitative increase" of green innovation, and that improving the quality of open government data platforms can strengthen its green innovation effect. In addition, this effect is also verified at the micro-firm level. The article provides useful insights for promoting high-quality open government data and green innovation in cities, and provides empirical references for exploring policy design that meets the development requirements of new quality productivity.