Research on green economic growth is gradually expanding into the transportation sector, but fewer studies have examined the relationship between the development of urban transportation infrastructure, such as subway systems, and green economic growth in cities. Based on the panel data of 41 metro-opening cities in China from 2007 to 2019, this paper attempts to answer whether and how the development of metro systems affects green economic growth in Chinese cities. The empirical study found that: (1) Metro system development significantly contributes to green economic growth at the city level. Each additional 100 Chinese miles (50 km) of metro system development can lead to a 2.2% increase in the green economic growth of the city. (2) In the robustness test, four methods are used to show that the empirical results are robust and reliable. (3) Heterogeneity analysis shows that the impact of metro system development on green growth varies according to the degree of connectivity of the metro system, the level of green economic growth, and the level of productive service industry agglomeration. (4) Mechanism analysis shows that the development of the metro promotes green economic growth through the advanced industrial structure, which has a significant partial mediating effect.