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A trimodal porous support with special trimodal pore structure has been prepared by physically mixing the silica gel (HPS) and SBA-15 and then devoted to fabricate TEPA-functionalized adsorbent for CO 2 capture. The trimodal multistage mesopores structure can promote the TEPA dispersion and mitigate the mass-transfer resistance in the adsorbent and, hence, improve capture performance, compared to the single mesoporous support. The influence of the mass ratios of HPS to SBA-15, amine loaded amount, CO 2 concentration, adsorption temperatures, and water vapor were studied. The CO 2 -saturated adsorption amount of 5.05 mmol/g was obtained at 75 °C in dry N 2 flow containing 15 vol % CO 2 when the mass ratio of SBA-15 to HPS was 1:2 with 50 wt % TEPA loadings. Moreover, the CO 2 -saturated adsorption amount presented a 16% improvement in humid N 2 flow containing 15 vol % CO 2 flow at 75 °C. In addition, the S2HPS-TEPA50% also demonstrated good stability after 10 adsorption/desorption cycles. Based on in situ DRIFTS results of CO 2 adsorption/desorption process, the reaction mechanism of CO 2 with active sites was proposed by analyzing the relationships among variations of intensities of functional groups during the reaction. The intraparticle diffusion model was adapted to study CO 2 kinetics and the intraparticle diffusion prediction indicated that boundary layer diffusion was the rate-controlling step in the process of CO 2 capture. Overall, these results indicate that S2HPS-TEPA50% is promising for CO 2 capture.