Abstract: The synergy of pollution and carbon reduction can measure environmental benefits and as well as climateand economic benefits, and will definitely become an inevitable choice to achieve comprehensive green transformation of economic and social development in the procedure of ecological civilization in China. As a major platform and important policy grip for the construction of ecological civilization in the new era, the establishment of national ecological civilization demonstration area is of practical significance to study the synergistic of pollution and carbon reduction to crack the real dilemma of tightening resource constraints, serious environmental pollution and ecosystem degradation. Based on the data from 209 prefecture-level cities in China from 2006 to 2019, a multi-period double difference and extended spatial forms was used to assess the synergistic effect of the pilot policy of national ecological civilization demonstration area on urban pollution and carbon reduction. The results showed that:(1) the pilot policy of national ecological civilization demonstration area significantly promotedthe synergistic of urban pollution and carbon reduction, and this finding is still valid after a series of robustness tests. (2) The Bacon Decomposition found that the "good treatment group" accounted for 98.33%, implying that the validity of the model setting was further verified. (3) The spatial spillover of the pilot policy showed the characteristics of "beggar-thy-neighbor". There existed significant differences among cities with different technology endowment, industrial agglomeration scale, and environmental regulation intensity.Accordingly,this paperproposed to promotethe orderly diffusion of pilot policies, optimizing the spatial layout of policies, and designing a gradient development strategy.