Abstract: In the era of environmental co-production, the public is expected to actively participate and play a role in supervision and governance. However, in reality, the public's enthusiasm for participation remains insufficient. As a key bridge connecting the government and the public, social organizations play an important role in promoting public participation, but the influencing factors and mechanisms of their role remain a "gray box" to be explored. To address this gap, an empirical study was conducted using a survey experiment. The results show that providing rich information and shaping social norms can effectively enhance the public's willingness to participate, while the effect of process simplification is not significant. The combined strategy of information and norms has a more obvious boosting effect, and the credibility of social organizations and environmental awareness can moderate the effect of information boosting. This study identifies the micro-mechanism by which social organizations stimulate public participation, providing a theoretical basis and policy implications for building a modern environmental governance system with extensive social participation and collaborative advancement. It also introduces the nudge theory into the field of environmental co-production, expanding the application scope of the nudge theory.