Abstract: We clarify the evolution characteristics of atmospheric environmental capacity of urban agglomerations in the middle reaches of the Yangtze River and provide technical support for scientific formulation of mitigation policies.Based on the regular observation data of meteorological stations from 1961 to 2016, the national standard method was used to calculate the atmospheric stability, mixed layer thickness and atmospheric environmental capacity coefficient of the midstream urban agglomeration in the past 56 years. The results show that in the past 56 years, the middle-stream urban agglomerations have basically been mostly neutral, followed by stable ones, and unstable ones the least. The frequency of the neutral class in the Wuhan city circle has a significant downward trend at -3.4％/10a, while the unstable and stable classes show a significant upward trend at 1.9％/10a and 1.5％/10a. The frequency of the unstable class in the city circle around Changsha-Zhutan and Poyang Lake have no obvious change; but the upward trend of the frequency of the neutral class is significant at 0.3％/10a and 1.2％/10a, and the stable frequency shows a significant downward trend at 0.3％/10a and 1.1％/10a. The thickness of the mixed layer of Wuhan urban circle in spring and summer is higher than that in autumn and winter; summer, of which during autumn and winter all show a downward trend at 0.1 m/10a, 6.0 m/10a and 43.9 m/10a, and that in spring shows an upward trend at 9.3 m/10a. The thickness of the mixed layer of the four seasons in the city circle around Changsha-Zhutan and Poyang Lake both declined. The atmospheric environmental capacity coefficient was in an inverted U-shaped distribution, with the peak value occurring in summer, and autumn and winter were periods of low values. In the 56 years, the atmospheric environmental capacity coefficient of each city circle has gradually declined at 1.6 ×10⁴,0.9×10⁴ and 1.8×10⁴（km²/a）/10a,corresponding to increased atmospheric stability, decreased thickness of the mixed layer, and decreased wind speed of the mid-stream urban agglomeration.