Abstract: This study examined the temporal and spatial changes of temperature inversion characteristics in the Sichuan Basin based on ERA5 hourly temperature profile data from 2000 to 2020.The temperature inversion's contribution to PM2.5 was quantified and temperature inversion characteristics and boundary layer structure were examined, during periods of high pollution in Chengdu and Yibin.Geographically, the eastern and southern regions had the highest frequency of temperature inversions (15%–25%), followed by the middle basin, while the northwest and southwest regions had the lowest frequency.The overall concentration of the seasonal change in temperature inversion thickness in the basin was between 200 and 350 m, with little variations in geographic distribution.The highest temperature inversion strength in the central region reached about 0.45  °C/100 m during the winter.The frequency, thickness, and intensity of temperature inversions at stations in the Sichuan Basin were all positively connected with PM2.5, with the correlation coefficients of 0.3, 0.28, and 0.25, respectively.When the temperature inversion thickness in Chengdu and Yibin was 376 m and 374 m, respectively, the average PM2.5 concentration reached about 75 μg/m3, and the fitting curve between temperature inversion intensity and PM2.5 concentration was parabolic, according to the fitting relationship between temperature inversion characteristics and PM2.5.In most cases, a continuous deep inversion layer was linked to high pollutant concentrations during periods of heavy air pollution.The PM2.5 concentration in Chengdu reached 163 μg/m3 and 157 μg/m3 on February 16 and 19, respectively, and the frequency and thickness of temperature inversions reached 70% and greater than 300 m.Additionally, there were double-layer temperature inversions.On January 19, 2017, the maximum concentration of PM2.5 in Yibin was 228μg/m3, and the temperature inversion frequency, thickness and intensity were 100%, 727.5m and 0.37  °C/100 m, respectively.In Chengdu and Yibin, relative humidity under the inversion layer reached 80–99% during this period of high air pollution, while the wind speed was less than 2 m/s near the surface.The formation of secondary fine particles and the buildup of primary PM2.5 were both influenced by the robust, stable boundary layer structure and high humidity.