To explore the aerosol chemical extinction during complex air pollution, a field campaign was carried out to investigate the composition and extinction characteristics of PM2.5 in spring when O3 and PM2.5 combined pollution occurred in Chengdu, China, and the relationship between chemical composition and extinction characteristics was studied using the chemical extinction algorithm proposed by IMPROVE in the United States. The results showed that the average concentration of PM2.5 and scattering coefficient bsp in the spring of 2018 in Chengdu were (50.3±22.4) μg·m－3 and (237.5±140.2) Mm－1, respectively, and both of them showed the similar diurnal variation trend with “single peak and single valley”. The extinction coefficient of spring PM2.5 in Chengdu was (268.4±153.7) Mm－1, and the chemical components that contributed the most to it were NH4NO3 (26.0%) and organic matter (OM) (24.4%). In the case of PM2.5 and O3 combined pollution, the mass of secondary pollution components (SNA, the sum of SO42－, NO3－, NH4+) and secondary organic carbon (SOC) increased significantly, which increased by 1.0 and 1.3 times respectively compared with the clean day, and OM became the largest extinction contributor (32.2%), followed by NH4NO3 and (NH4)2SO4, contributing 22.8% and 20.5% respectively. Therefore, it is shown that further reducing the emission of precursor gases such as SO2, NOx, NH3 and VOCs may be efficient to improve the air quality and visibility in Chengdu district.