Abstract: Air pollution has gradually become an important issue, and has attracted more and more attention from the general public and the scientific community. How do different cities interact with each other with respect to the air quality issue? What is the similarity and difference among the air quality attributes of distinct cities, and what factors may influence the interaction? We answer these intricate questions by proposing a comprehensive visual analysis system to explore the evolution of an urban agglomeration. The method proposes a Voronoi diagram to show the spatial distribution of urban agglomeration and the evolution of urban agglomeration in space, a stacked graph with threads embedded to show urban agglomeration in the time evolution process, and a parallel coordinates diagram to show the pollution situation of urban agglomerations. We have applied our method to the real urban air quality data. Our system was used to explore the evolution of urban agglomeration and provide a necessary foundation for united pollution prevention of urban agglomerations.