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, 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, CO2 concentration, adsorption temperatures, and water vapor were studied. The CO2-saturated adsorption amount of 5.05 mmol/g was obtained at 7S degrees C in dry N-2 flow containing IS vol % CO2 when the mass ratio of SBA-15 to HPS was 1:2 with 50 wt % TEPA loadings. Moreover, the CO2-saturated adsorption amount presented a 16% improvement in humid N-2 flow containing 15 vol % CO2 flow at 75 degrees C. In addition, the S2HPS-TEPA50% also demonstrated good stability after 10 adsorption/desorption cycles. Based on in situ DRIFTS results of CO2 adsorption/desorption process, the reaction mechanism of CO2 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 CO2 kinetics and the intraparticle diffusion prediction indicated that boundary layer diffusion was the rate-controlling step in the process of CO2 capture. Overall, these results indicate that S2HPS-TEPA50% is promising for CO2 capture.