Abstract: To deal with the COVID-19 outbreak, Kunshan has strictly followed the national epidemic prevention regulations and implemented strict lockdown measures since January 24, 2020. Air quality has altered as a result of decreased anthropogenic emissions, particularly those caused by motor vehicles. Based on the environmental monitoring network combined with the meteorological observation system, the integrated use of mathematical statistics and spatial analysis techniques has been applied to investigate the effect of variations in human activity patterns on the air quality of Kunshan before (January 1–20, 2020) and during the lockdown (January 27–February 15, 2020). The results demonstrated that great progress had been made in pollution control compared with the same period (January 1–February 15) in the past three years, revealing that the days when particulate matter (PM_2.5 and PM₁₀) exceeded the standard have reduced by 4 days. The daily maximum 8-h ozone (O₃) concentration (MDA8 O₃), however, has increased by 14%, revealing that severe O₃ pollution is expected to be an issue throughout the whole year rather than limited to the summertime. Due to the reduction of emissions mainly from the transportation sector during the lockdown, the concentration of nitrogen dioxide (NO₂, an important precursor of O₃) and particulate matter reduced considerably, while MDA8 O₃ increased by 62%. It was discovered that severe pollution events may occur even in the case of emission reduction; therefore, the effect of meteorological conditions on air quality cannot be ignored. The effect of meteorological conditions on air quality cannot be overlooked because it has been discovered that significant pollution events can still happen even when emissions are reduced. Furthermore, this study improves the insights into the characteristics of the main pollutants in Kunshan in winter and investigates the impact of anthropogenic emissions and meteorological factors on pollutants, which will provide a scientific reference for the simulation and prediction of aerosol at an urban scale in the Yangtze River Delta, China.