ABSTRACT ‘Ecological symbiosis’ depicts the phenomena of dynamics, interconnection and coevolution of participants within an ecosystem. The concept has been widely applied in recent years to describe the theory framework of ‘Regional Innovation Ecosystem’ (RIE). This study has two goals. The first is to clarify the formation of ‘Regional Innovation Ecosystem’ (RIE) from an ‘ecological symbiosis’ perspective. The second is to explore the impact of RIE on ‘Outward Foreign Direct Investment’ (OFDI) in emerging economies. We construct an evaluation system for RIE based on a dataset of Chinese cities from 2009 to 2019 and calculate the symbiosis index of RIE using the entropy method. Our finds identify the determinants in the formation of RIE and depict the spatial heterogeneity characteristics of Chinese RIEs. Empirical evidence indicates that RIE symbiosis significantly promotes OFDI by local firms, especially technology-seeking OFDI. Implications of innovation policy and strategic management are discussed, such as high-tech zone construction, technological innovation atmosphere, government-industry-university collaborative innovation strategy and strategic overseas investment layout.