Abstract: The '2+26' cities in Beijing-Tianjin-Hebei and its surrounding areas are the transmission channels of air pollution in the Beijing-Tianjin-Hebei areas and also one of the most serious air pollution cities in China. The PM_2.5, PM₁₀, SO₂, NO₂, O₃ and CO data from 2013 to 2019 released by China National Environmental Monitoring Centre (CNEMC) were selected in this paper to describe the characteristics of air pollution of '2+26' cities, and the factors influencing urban air quality were discussed. The results showed that the air quality of '2+26' cities generally tended to improve as the concentration of PM_2.5, PM₁₀, SO₂, CO and NO₂ decreased by 50%, 41%, 79%, 49% and 20%, respectively, in 2019 compared with 2013. However, the 90th percentile of the daily maximum 8-hour average ozone concentration (O₃-8 h-90per) increased by 21%. From 2013 to 2019, the number of heavy pollution days in the '2+26' cities continued to decrease, and it decreased by 67% in 2019 compared with 2013. The number of serious pollution days decreased by 90%. Although the proportion of excellent days had increased, it had basically stabilized at about 50% after 2016, and there was no continuous increasing trend. The highest concentrations of PM_2.5, PM₁₀, SO₂, NO₂ and CO all appeared in January, while the highest concentration of 8-hour average ozone concentration (O₃-8 h) appeared in June. The higher the PM_2.5 concentration, the higher the ratios of PM_2.5/PM₁₀ and SO₂/NO₂, and the greater the contribution of secondary pollution sources and coal-fired sources to PM_2.5. In terms of spatial distribution, the areas with high PM_2.5 and PM₁₀ were mainly concentrated in the plains in front of the Taihang Mountains, and the low concentration areas were mainly concentrated in the north of the Beijing-Tianjin-Hebei areas. Geographical location, meteorological conditions, industrial structure, energy consumption intensity and emission reduction policies were important factors affecting the air quality of '2+26' cities from 2013 to 2019. With the strengthening implementations of air pollution prevention and control measures, the emission reduction policies have become the most important measure to the air quality improvement in '2+26' cities in the Beijing-Tianjin-Hebei and its surrounding areas.