Air pollution in Yunnan province in spring has been prominent in recent years, which becomes a key resistance for defending the blue sky. Evolution characteristics of air quality and the impacts of meteorological factors and biomass burning in foreign regions on air quality in Yunnan province during spring 2018-2021 were analyzed comprehensively, based on ground monitoring data and satellite remote sensing data. The results revealed that the non-attainment days had reached up to 262 days (including 6 heavy pollution days) in spring in the past four years, accounting for 91.3% for all cities and 96.8% in southern Yunnan of the whole year. For temporal distribution, the pollution was concentrated in mid-March to mid-April, and the heaviest was in 2019, followed by 2021 with decreasing excellent days and increasing fine days significantly. In 2020, the pollutant concentration was the lowest, but heavy pollution occurred for 6 days. For spatial distribution, the pollution in southern Yunnan was far higher than that in central and northern Yunnan, with the highest in Xishuangbannan accounting for 27% of all non-attainment days; but the ozone (O3) concentration is the highest in southwest and central Yunnan, with the highest in Pu’er. PM2.5 was the dominant primary pollutant during 2018-2021, but the proportion of O3 as the primary pollutan in 2018 and 2019 was a little higher than that of PM2.5. Generally, the relationship of PM2.5 and O3 shown a significantly positive synergistic effect, and high O3 levels promoted secondary generation of PM2.5. PM2.5 and O3 pollution was both associated with less precipitation and southwest wind; furthermore, combined with mid-high temperature and mid-low humidity, O3 pollution easily occurred, and PM2.5 pollution was related with mid-high temperature and mid-high humidity, and mid-high temperature and mid humidity caused synergistic pollution of O3 and PM2.5. Highest pollution in 2019 was associated with the highest temperature and the least precipitation. Air pollution in Yunnan was significantly positive correlated with the number of fire points in the day and 1-3 day lags, and the highest correlation for PM2.5 and O3 were 2 day lag and 1 day lag, respectively. Ultimately, in unfavorable meteorological conditions dominated by the southwestern monsoon, biomass burning in foreign regions, especially Myanmar in Indo-china Peninsula is the main source for air pollution in spring in Yunnan, which enhanced the secondary generation of air pollution. Thus, these results indicated that the focus of spring pollution control in Yunnan is to establish a perfect cross-border air pollution prevention and control mechanism and to strengthen the early warning of biomass burning in foreign regions under unfavorable weather conditions.