Can two-way FDI synergy promote regional high-quality green development under environmental decentralization?

China's high-level opening-up benefits its economic growth. The significance of supporting regional high-quality green development by enhancing foreign capital use and outbound foreign investment has grown in recent years. This paper develops a regional development assessment system and calculates the index of each region by using entropy method. Then, it introduces a capacity coupling system model to measure the two-way FDI synergy. Finally, it employs the spatial model that was developed to assess the synergy's influence on regional green development under the environmental decentralization. According to the findings, the synergy can improve the local development. However, it inhibits the improvement of economic development quality in neighboring regions. In addition, environmental decentralization negatively moderates the synergy's on the local development. Therefore, the central government needs to implement targeted economic policies to shorten the development gap between regions, fully use the positive role of environmental decentralization and improve the local development.