The outbreak of 2019 novel coronavirus (COVID-19) has hugely impacted the world and becomes a global public threat. To prevent the spread of COVID-19, human activities are largely restricted in China in early February, 2020. The influence of strict COVID-19 control policies on air quality and the potential influence of particulate matter concentration on COVID-19 infection in China are of great interest. This study analyzes the concentrations of six major air pollutants in 366 urban areas across mainland China during January 1 to April 30 in 2017-2020. Results show that strict COVID-19 control policies have significantly improved the air quality in many provinces. Compared to 2019, national mean concentrations of PM_(2.5), PM_(10), SO_2, NO_2 and CO in 2020 decrease by 14%, 15%, 12%, 16% and 12%, respectively, while the concentration of O_3 increases by 9%. Generally, the diurnal variation of PM_(2.5) and PM_(10) concentrations remains unchanged during COVID-19 and their concentrations are high in the morning and evening while low in the afternoon. Correlation analysis shows that daily COVID- 19 infections are positively correlated with PM_(2.5) concentration in many provinces, indicating a potential risk of aerosol transmission in high PM_(2.5) environment. Thus it is suggested to stay at home in highly polluted days and go out in the afternoon to reduce the risk of infection due to aerosol transmission.