In grassroots water environment governance, political–community dialog is an unavoidable issue. Traditional policy analysis tools emphasize top-down stages and sequences, often ignoring the essential role of social factors (organizations, resources, or individuals)—outside the policy subsystem—in policy advocacy. The Advocacy Alliance Framework (ACF) provides a perspective on the role of social factors in policy changes and the interaction mechanism driving the relevant stages and alliances. In this study, we re-examine the key elements of the ACF and extract the grassroots logic of policy advocacy by discussing how actors act from policy divergence to policy learning, constructing an action framework to explain grassroots social policy advocacy in China. We find that policy advocacy depends on the joint influence of multiple elements such as the alliance members, alliance belief system and alliance resources. Therefore, social forces can better intervene in the policy agenda and achieve effective political–community dialog by identifying the relevant elements.