The Belt and Road Initiative (BRI) significantly contributes to the world economy. However, the central part of the Belt and Road (B&R) is located in fragile ecological zones that are arid, semi-arid, or sub-humid. Using the entropy method, the economic-social-natural ecological niches and their coupling coordination during 2007–2019 along B&R’s 11 countries were explored along with regional differences and spatiotemporal characteristics. The economic-social-natural ecological niches were low, with a fluctuating upward trend. Additionally, the average annual growth rate of the synthesis ecological niche dramatically improved after the BRI. Further, the BRI facilitated inter-country trade and promoted the economic ecological niche. However, the BRI marginally affected the social ecological position, possibly because the social ecological niche was high pre-BRI. The natural ecological niche showed a negative growth after the BRI. Further, the coupling coordination of economic-social ecological niche and natural ecological niche showed an upward trend, transforming from severe discoordination to advanced coordination. Although BRI promoted advanced coordination, it did not affect internal categories. Policy recommendations for sustainable development in China-ASEAN Free Trade Area were provided. This study can assist policymakers to balance economic-social development and environmental protection.

There is growing concern about carbon emissions as the economy grows, which is of great importance to the implementation of the green Belt and Road Initiative (BRI) development strategy. Using panel data of 282 prefecture-level cities in China from 2006–2020 and the difference-in-differences method, this paper empirically examines the effects of the BRI on carbon emissions. Both theoretical and empirical analyses indicate that the BRI can significantly reduce the carbon emission level of cities along the routes, but the impact varies in different regions and cities. The mechanism analysis shows that the BRI reduces the carbon emission level of the Belt and Road cities through the economic agglomeration effect and industrial structure effect. Therefore, China should vigorously promote green Belt and Road construction, implement a regional integration strategy, and promote the transformation and upgrading of the industrial structure. These findings have a certain reference value for the follow-up implementation of the BRI.