Binary adsorption of benzene and supercritical carbon dioxide on the carbon of a slitlike pore was theoretically studied by the nonlocal density functional theory (NDFT) of Kierlik and Rosinberg. The interaction between adsorbate molecules was represented by Lennard-Jones potential, and the 10-4-3 model was applied for the solid-fluid interaction. The effects of temperature, pressure, and bulk mole fraction of benzene on the adsorption behaviour of the supercritical CO2 fluid mixture were investigated. The bulk fluid density is found to be the main controlling factor determining the adsorption at higher pressure, and comparatively, the adsorption is only weakly dependent upon temperature. The variation of the binary adsorption with the pore width was calculated, and the adsorption packing mechanism is discussed. The calculated results suggest that an optimal pore structure of adsorbent is possible for an enhancement of benzene adsorption. Finally, by applying the NDFT modeling result to the experimental data, a pore size distribution (PSD) of real material is characterized. The validity of the obtained PSD is evaluated and analyzed.