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 no...