Our　study　employs　panel　data　from　272　Chinese　prefecture-level　cities　(2003–2020),　leveraging　the　“Civilized　City”　selection　campaign　as　a　quasi-natural　experiment.　Using　a　Spatial　Durbin　Difference-in-Differences　model,　we　systematically　analyze　the　policy’s　impact　on　local　environmental　governance　performance　and　its　spatial　spillover　effects,　with　rigorous　robustness　checks.　Results　reveal　a　significant　positive　spatial　correlation　in　China’s　environmental　governance　performance,　indicating　interdependence　among　cities　rather　than　isolated　decision-making.　The　“Civilized　City”　initiative　not　only　improves　local　environmental　governance　but　also　generates　spillover　benefits　for　neighboring　regions,　thereby　enhancing　coordinated　regional　sustainability.　Finally,　we　propose　policy　recommendations　grounded　in　empirical　findings　and　China’s　governance　context.　©　2025　by　the　authors.