Abstract: The air pollution characteristics were analyzed during the coronavirus disease (COVID-19) in Beijing. The hybrid single particle lagrangian integrated trajectory (Hysplit), potential source contribution function (PSCF), and concentration weighted trajectory (CWT) were also applied to study the main transport pathways and potential source regions of air masses during heavy pollution. Results show that compared with before COVID-19 (January 1-22, 2020) and the same period of 2019, the concentration of PM_2.5 (aerodynamic diameter of < 2.5 μm) after COVID-19 (January, 23-31, 2020) increased by 149.7% and 62.2%, respectively, while increased by 40.6% and 6.8% for sulfur dioxide (SO₂), 42.6% and 37.8% for carbon monoxide (CO), and 73.6% and 28.0% for ozone (O₃). Nitrogen dioxide (NO₂) concentrations after COVID-19 decreased by 27.9% and 21.6%, respectively, compared with before COVID-19 and the same period of 2019. The most polluted day in January 28 was selected to analyze the backward trajectory and potential source regions. The air masses from the surrounding of Beijing were the main transport pathways of heavy pollution episode. The main potential source regions mainly concentrated in Beijing, northern Langfang, and northern Tianjin. The long-distance transmission from central and western Inner Mongolia and northern Beijing had little impact on this heavy pollution episode. Therefore, it is still necessary to conduct the regional joint prevention and control to improve the air quality in Beijing.