There is a global need to jointly build the green Belt and Road Initiative (BRI) in order to develop a philosophy of ecological civilisation and achieve sustainable development. This paper aims to analyse the temporal and spatial characteristics of the green development cooperation (GDC) network among BRI regions and countries and explore the reasons for its formation. To this end, the first step was to analyse the spatial and temporal characteristics of green development capability in six regions of 104 BRI countries from 2013 to 2019 using the synthetic evaluation model and entropy method. Next, social network analysis was used to analyse three characteristics of the GDC network: network structure, node structure, and community structure. Moreover, the indicators of network strength and network correlation were used to estimate the structural characteristics of the entire GDC network, while degree centrality, betweenness centrality, and closeness centrality were used to estimate the role and status of countries in the GDC network. In addition, modularity optimisation was used to analyse the community structure and regional effects of the GDC network. The results show that (1) the green development capability of the BRI countries has spatial and temporal heterogeneity. (2) The GDC network among the BRI countries has been initially formed, and has the characteristics of high connectedness, high efficiency, low density, and low hierarchy. (3) The GDC network has community structure and regional effect, showing polycentric and hierarchical characteristics. (4) China, Russia, and the European countries have stronger radiating and controlling power. Central Asian countries along the land Silk Road and Indian Ocean countries along the maritime Silk Road play a significant role as intermediaries and bridges, while the BRICS and Shanghai Cooperation Organisation (SCO) countries play a vital role as the central actors. Finally, some theoretical and practical implications are put forward to provide a blueprint for jointly achieving the sustainable development goals.