<p>Enhancing the synergy level of pollution and carbon reduction in cities is the key to mitigating air pollution and climate warming in China. This study used quantitative assessment methods and geographical detectors to investigate the spatial and temporal evolution characteristics and driving factors of the synergy level of air pollution and carbon reduction in the “2 + 36” cities (Beijing-Tianjin-Hebei and nearby cities in China). The results revealed that: (1) Emissions of air pollutants decreased by 22.2% during the study period, but carbon dioxide emissions increased by 10.0%, with only nine cities achieving synergies in reducing pollution and carbon. (2) The synergy level in the study area was low (-3.8% to 1%), and the spatial distribution was characterized by heterogeneity and clustering. (3) The effects of wind speed and technology expenditures on the level of synergy were particularly strong, and the two—factor interaction showed a decreasing dominance of natural factors and a rising importance of energy factors and human capital. These findings provide a basis for the targeted development of city-scale action programs for air pollution and carbon reduction.</p>