Abstract: Diesel mobile combustion sources, including diesel vehicles and diesel machinery, are the key sources for further sustainable air quality improvement in China at this stage. To explore the pollution emissions of diesel mobile combustion sources in the Beijing-Tianjin-Hebei (BTH) region and their emission reduction potential, this paper set up a baseline scenario and five policy scenarios based on estimating the current status of diesel vehicle and diesel machinery pollution emissions in the Beijing-Tianjin-Hebei region in 2018, predicted the pollution emission trends of diesel combustion sources under different scenarios from 2019 to 2030, and compared and analyzed the pollutant emission reduction potential of different regions and sources. Results show that the emission reduction potential of diesel combustion sources in the Beijing-Tianjin-Hebei region in 2019-2030 will be reduced and the emissions of CO, HC, NO_x and PM from diesel combustion sources in the Beijing-Tianjin-Hebei region in 2018 are 512 500 t, 228 900 t, 1 065 200 t and 54 200 t, respectively. The combined scenario can reduce CO, HC, NO_x and PM pollutant emissions in 2030 by 52.03%, 38.58%, 71.88% and 52.07%, respectively, compared with that in the base year. The emission reduction effect of the scenario of phasing out high emissions is more effective in a short period of time, while the long-term effect is less effective. The emission reduction potential of the scenario of improving emission standards and promoting new energy will increase year by year, which has a better emission reduction effect on pollutants, and the emission reduction potential of the scenario of transporting public to railway is also better, which can effectively reduce 35.13%-45.81% of pollution emissions in 2030. The maximum reduction potential for diesel vehicles and diesel machinery under the combined scenario is 91.55% and 44.69%, respectively. In addition, the emission reduction potential of CO and NO_x mainly comes from diesel vehicles, while diesel machinery has a significant reduction effect on HC and PM. Compared with the other two regions, Tianjin has a better pollution emission reduction effect with a maximum emission reduction potential of 80.80%. By type, diesel trucks contribute more to the emission reduction of pollutants, especially heavy trucks. Compared with construction machinery, the pollution emission reduction contribution of agricultural machinery is greater, especially the emission reduction contribution of combine harvesters, agricultural water pumps and tricycles. This study can provide scientific support for the development of pollution control policies for diesel mobile sources.