Based on the quasi-natural experiment of the key city policy of air pollution control implemented in 2003, this paper analyzes the impact of air pollution regulation on urban air pollution control from the regional level by using Differences-in-Difference model. The results show that:(1) air pollution regulation significantly reduce the intensity of industrial sulfur dioxide emission, industrial sulfur dioxide emission and PM2.5 annual concentration in key cities. (2) In the nine years after the implementation of the policy, 122.158 million tons of urban industrial sulfur dioxide emissions have been effectively reduced, and the average annual concentration of PM2.5 has been improved by 2.97 μg/m³, with the reduction ratio of 36.2% and 8.5% respectively. The average annual sulfur dioxide emission of urban industry has been reduced by 3.7% and the urban PM2.5 concentration has been reduced by 0.944%. (3) The key city policy of air pollution prevention and control for urban air pollution control is mainly realized by reducing energy consumption, increasing the intensity of urban pollution control, promoting the transformation and upgrading of regional industrial structure and improving the level of production technology.