Abstract: Yunnan Province is located in a low-latitude plateau area adjacent to Southeast Asia. The local emissions and air quality of this province are affected by cross-border transportation from Southeast Asia. This study analyzes the observational PM2.5 concentration data from 2017 to 2021 at 40 sites in 16 cities of Yunnan Province to understand the characteristics and trends of PM2.5 pollution. Cluster analysis with the HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) backward trajectory model and concentration weighted trajectory are used to analyze potential PM2.5 sources. The results show that the annual mean PM2.5 concentration in Yunnan Province decreases by 0.91±0.23 μg m⁻³ a⁻¹. PM2.5 concentration varies seasonally, and its concentration reaches the highest value in spring with 31.92±9.08 μg m⁻³ and lowest in summer with 13.50±2.69 μg m⁻³. The PM2.5 pollution is severe in spring due to biomass burning in Southeast Asia, which contributes to ＜40 μg m⁻³ of PM2.5 concentration. The high-potential source areas in spring include the southwest of Guangxi. The diurnal PM2.5 variations reveal a bimodal pattern with the value peaking between 0900 LST–1200 LST and 2100 LST–0100 LST, which is mainly attributed to human activities and meteorological factors, such as the lower boundary layer height and wind speed. In conclusion, PM2.5 during spring in Yunnan Province mostly comes from cross-border transportation. Thus, this study provides new insight for air pollutant control in the province.