Abstract: The effects of coexistent gaseous components and fine particles on the CO₂ separation performance by polydimethylsiloxane/polysulfon (PDMS-PSF) flat sheet composite membranes were investigated in a simulated test-bed. It can be found that O₂ slightly inhibits the CO₂ separation performance, while the effect of SO₂ is negligible during the test time due to its low concentration in the flue gas. Water vapor promotes the CO₂ separation performance of PDMS-PSF composite membranes. The fly ash fine particles significantly deteriorate the CO₂ separation performance of PDMS-PSF membranes. Moreover, the CO₂ separation experiments by PDMS-PSF membranes with an actual flue gas from a desulfurization system of the coal-fired hot testing facility were conducted for 50 h. At the beginning, the CO₂ separation performance is slightly improved due to the combined effect of water vapor, O₂ and SO₂. With the extension of the test time, the impact of the fine particles deposited on the membrane surface increases, which gradually deteriorates the CO₂ separation performance of PDMS-PSF membrane. The CO₂/N₂ selectivity and the CO₂ permeation rate are decreased by 17.91% and 28.21%, respectively.