Abstract: In recent years, air pollution in Yunnan Province during spring has emerged as a major challenge in attaining optimal air quality. This work comprehensively analyzes the evolution characteristics of air quality and the impacts of meteorological factors and biomass burning in foreign regions on air quality in the Yunnan Province during spring from 2018 to 2021. The analysis is based on ground monitoring data and satellite remote sensing data. The results showed that in the past four years, the nonattainment days in spring approached 262 d (including six heavy pollution days), accounting for 91.3% for all cities and 96.8% in southern Yunnan for the whole year. In terms of temporal distribution, the pollution was concentrated in the period spanning mid-March to mid-April, with the heaviest in 2019 followed by 2021, which resulted in a considerable decrease in days with good air quality and an increase in days with moderate air quality. In 2020, pollutant concentration was the lowest, and heavy pollution occurred over a span of 6 d. Spatially, southern Yunnan experienced significantly higher pollution than central and northern Yunnan, with Xishuangbanna accounting for 27% of all nonattainment days. However, ozone (O₃) concentration was highest in southwest and central Yunnan, with the highest in Pu’er. From 2018 to 2021, PM2.5 was the prevalent primary pollutant, although the proportion of O₃ as the primary pollutant was slightly higher in 2018 and 2019. To this end, PM2.5 and O₃ were synergistically correlated, and high O₃ levels promoted the secondary generation of PM2.5. Both pollutants were associated with low precipitation and southwest wind. O₃ pollution was most likely to occur during mid-high temperatures and mid-low humidity, whereas PM2.5 pollution was associated with mid-high temperatures and mid-high humidity. However, mid-high temperature and mid humidity resulted in synergistic pollution of O₃ and PM2.5. In 2019, the highest pollution levels coincided with the highest temperature and the lowest precipitation. Air pollution in Yunnan was influenced by open biomass burning, and pollutant concentrations had a remarkable positive correlation with the number of fire points at lag 0-3 d. The highest correlations for PM2.5 and O₃ were observed at lag 2 d and lag 1 d, respectively. In unfavorable meteorological conditions dominated by the southwestern monsoon, biomass burning in foreign regions, particularly in Myanmar in the Indochina Peninsula, is the primary source of air pollution during spring in Yunnan. This biomass burning enhances the secondary generation of air pollution. Therefore, the focus of spring pollution control in Yunnan should be on establishing a perfect cross-border air pollution prevention and control mechanism and strengthening the early warning system for biomass burning in foreign regions under unfavorable weather conditions.