Abstract: The '2+26' cities are one of the key areas in the implementation of air pollution prevention and control in China. In order to quantitatively evaluate the achievements of ecological civilization construction in '2+26' cities, based on the research of national ecological civilization development level evaluation, this study further improved the evaluation method, and evaluated the ecological civilization development level of '2+26' cities in 2015 and 2017 by the double benchmark progressive method, revealed the short boards of the regional ecological civilization development, compared and analyzed the interannual change of the ecological civilization development level from 2015 to 2017 and its main reasons, especially the impact of air quality improvement on the regional ecological civilization development level. The results show that: (1) In 2017, the eco-civilization China (ECC) score of the '2+26' cities was 64.98. Compared with the Yangtze River Delta (YRD) Region, Pearl River Delta (PRD) Region, other urban agglomerations and the whole country, the development level of ecological civilization in the '2+26' cities remains relatively backward, and some shortcomings such as poor quality of the ecological environment, uncoordinated and unplanned development of regional urban and rural areas, uncoordinated economic development and environmental protection persist. (2) From 2015 to 2017, the ecological civilization development level of the '2+26' cities registered significant improvements, and the ECC score increased by 3.64 points. The surface water environment quality, the emission intensity of main water pollutants, and the emission intensity of main air pollutants were the main contributory factors. (3) From 2015 to 2017, there was no remarkable improvement in the air quality in the '2+26' cities, and their contribution to the improvement of ecological civilization development level was relatively insignificant, which may be related to the changes in meteorological conditions and the lag effect of air governance effect. The research results show that the development of ecological civilization in the '2+26' cities has achieved astounding success, but several shortcomings outstand. It is necessary to optimize the national ecological space, transform the economic development model, establish a coordinated development mechanism to remove the shortcomings, and further enhance the development level of ecological civilization.