Abstract: In the context of urban river ecological environment governance, a new paradigm of "diversified" governance entities has emerged. The market and social stakeholders are involved in this new paradigm. However, these multiple stakeholders have not yet reached an optimal state of co-governance. Exploring the determinants of multi-stakeholder co-governance can help overcome the operational dilemmas of this governance model and improve the urban river ecological environment governance system. From the perspective of dynamic governance, the collaborative process of multi-stakeholder co-governance in urban river ecological environment is divided into two stages: "formation" and "maintenance". Based on the SFIC model, a theoretical model of the influencing factors for multi-stakeholder participation in urban river ecological environment governance was constructed in this study. Using questionnaire survey data from the Yangtze River Delta region and employing Partial Least Squares Structural Equation Modeling (PLS-SEM) and Fuzzy-Set Qualitative Comparative Analysis (fsQCA), an empirical analysis of the pathways and configurations of influencing factors was performed in this paper. The research findings indicated: (1) in the "formation" stage of multi-stakeholder co-governance relationships, trust among stakeholders, market cooperation, social cooperation, and environmental information disclosure had a significant positive impact on multi-stakeholder participation in urban river ecological environment governance. Meanwhile, expected returns, governance capacity, market cooperation, and environmental information disclosure had a significant positive effect on the "maintenance" of multi-stakeholder co-governance relationships. (2) Trust among stakeholders, high governance capacity, expected returns, market cooperation, social cooperation, and environmental information disclosure could not individually serve as necessary conditions for the "formation" and "maintenance" of multi-stakeholder co-governance in urban river ecological environment. There was a need to consider their combined effects with other factors in exploring the way these factors exerted influence. (3) There were 4 equivalent causal paths that promoted the formation of multi-stakeholder co-governance in urban river ecological environment and 3 equivalent causal paths that promoted its maintenance. The effective combination of multiple factors promoted the development of multi-stakeholder co-governance in urban river ecological environment in a "different paths, same destination" manner. The research findings provided decision-making references for the sustainable governance of urban river ecological environments.