To explore the spatiotemporal coupling mechanism of the water network in the Erhai Basin under the combined influence of natural and social drivers, and to reveal the mediating role of topological features between driving factors and water system elements, this study integrates four phases of remote sensing and geographic data within the framework of complex network theory. Nine topological indicators were selected to characterize the structural features of the basin’s water network，to overcome the limitation of traditional regression that it is difficult to simultaneously handle driver collinearity, spatial overflow and mechanism decomposition, this paper constructs a （Partial Least Squares）PLS-（Spatial Durbin Model）SDM-（Mediation effect）MED framework that can handle multi-driver collinearity, simultaneously characterize spatial overflow, and decompose the total effect into direct effects and indirect effects conducted through topological structure, thereby more accurately identifying key intermediate paths. The results show that:(1) From 2001 to 2023, the Erhai water network evolved from a multi-source redundant configuration to a stable state characterized by a clear mainstem and relatively high efficiency.(2) Among a total of 216 paths, 68 significant X-M-Y paths were identified, with mediation efficiencies mainly ranging between 40% and 80%. Betweenness centrality of edges, compactness, global efficiency, and algebraic connectivity were identified as the core mediating indicators.(3) Social factors primarily exerted high-proportion negative effects on hydrological elements through the mediating role of network topology, while natural factors generally displayed moderately strong and stable positive effects, with a few pathways showing structural suppressing effects.The proposed PLS–SDM–Med analytical framework provides a transferable approach for identifying key structural units and risk pathways in plateau lake basins, offering a theoretical basis for zoning control and ecological restoration in the Erhai Basin and other similar highland lake watersheds.