The quantitative analysis of ground-based observations of atmospheric aerosols is a basic way to understand the optical properties of aerosols and the characteristics of atmospheric pollution， which can provide a certain basis for exploring the direction of pollution control.In recent years， there are few studies on the analysis of aerosol optical properties in different regions of Gansu Province using ground-based observations.In order to understand the atmospheric aerosol optical characteristics of different land surfaces in Gansu Province， we obtained the aerosol optical depth （AOD） of four stations in Gansu Province through ASTPwin software based on CE-318 solar photometer observations from April 2018 to September 2020 and calculated the Angstrom wavelength index α.The distribution and variation characteristics of AOD and α in different regions of Gansu Province in different seasons and the relationship between aerosol optical depth and wavelength index were analyzed.The results show that： （1） the changes of AOD in each wavelength band tend to be consistent in all stations during the observation period， and the AOD value decreases with increasing wavelength.The AOD values of Lanzhou and Gaolan Mountain were the highest in winter， followed by spring and autumn， and the lowest in summer.The winter and spring AOD values of Lanzhou exceeded the annual average by 14.98% and 4.68%， respectively， and the winter AOD value of Gaolan Mountain exceeded the annual average by 3.88%.Dunhuang and Minqin both had the highest AOD values in spring， which were 24.49% and 26.30% higher than their respective annual averages.The seasonal distribution of AOD in Dunhuang was： spring > summer > winter > autumn， while Minqin showed a trend of gradually smaller values from spring to winter.（2） The dominant particles in Lanzhou and Gaolan Mountain are coarse modal in spring and summer， while fine particles dominate in autumn and winter.Dunhuang and Minqin atmospheric aerosols are dominated by coarse modal particles all year round.In the winter of 2019， the AOD value of Lanzhou was 68.0% higher than that of Gaolan Mountain； Dunhuang and Minqin had more serious sand and dust aerosol pollution in spring 2019， and the AOD value of Dunhuang exceeded that of Minqin by 42.42%.（3） The frequency distribution of AOD and α at all sites showed a single-peaked curve， with variability in the range of high-frequency distribution of AOD in different seasons， but they were all below 1.0.The distribution of high-frequency range of α was more complex， with the range of α distribution less than 1.0 in spring in Lanzhou， spring and summer in Gaolan Mountain， four seasons in Dunhuang， and spring， summer and autumn in Minqin， while α in summer， autumn and winter in Lanzhou， autumn and winter in Gaolan Mountain， and winter in Minqin was mainly distributed at 1.1 or above.（4） The relationship between AOD and α differs in different seasons， which shows that the size of the dominant particles of aerosol differs in different seasons when the atmosphere is seriously or locally polluted.In spring when the atmosphere is in local or serious pollution and in summer when the atmosphere is in local pollution， the aerosols at the four stations are mainly large particle size， with the contribution of sand and dust aerosols being larger.In summer when the atmosphere is in serious pollution， Gaolan Mountain aerosol is mainly fine mode particles， Lanzhou， Dunhuang and Minqin aerosol is still controlled by coarse mode， but the proportion of pollution caused by small particle size in Lanzhou is higher than the remaining two stations， of which more than 85% belongs to urban industrial - aerosol pollution.In autumn， when the atmosphere is in serious pollution， Lanzhou and Gaolan Mountain are both dominated by fine modal particles， of which urban industrial-aerosols account for a significant increase， while Dunhuang and Minqin are still dominated by coarse modal particles， of which dust aerosols account for a large proportion.In winter， Lanzhou is still dominated by fine modal particles， while the other three stations are dominated by coarse modal particles.In winter， Dunhuang and Minqin are dominated by coarse and fine modal particles， while Gaolan Mountain is dominated by fine modal particles when the atmosphere is locally polluted.The analysis shows that， in general， aerosol pollution in the northern part of Gansu is dominated by sand and dust aerosols， while aerosol pollution in the southern part of Gansu shows alternating coarse-mode and fine-mode particles， which provides some references for the next study of aerosol properties and atmospheric pollution characteristics in different regions of Gansu by combining satellite remote sensing data.