Based on the case study of the "no garbage in the whole area" special governance initiative in Town A， western Sichuan，this paper employs the analytical framework of “institutional positioning” to examine how governance actors occupy different positions within the institutional structure at various stages，and how their scope of action， policy instruments， and capacities differ accordingly. It further analyzes the mechanisms through which institutional positioning influences collaborative governance. The results show that the institutional positions of governance actors have undergone a transformation from "dislocation" to "adaptation" in the process of environmental governance. The compatibility of institutional positioning represents a dynamic process in which actors dynamically adjust their positions according to goal-oriented needs， thereby driving a shift in governance mode from "unidirectional administrative governance" to "bidirectional embedded governance". Moreover， institutional positioning promotes collaborative governance through three interrelated mechanisms： institutional constraints and incentives， resource allocation and integration， and relational adjustment and reconstruction. In the process of grassroots governance， accurately identifying and optimizing the institutional positions of actors is conducive to achieving effective collaborative governance.