In this work, activated carbon models modified with different hydroxy contents were constructed by implanting hydroxyl groups at the edges of coronene. The physical properties, atomic partial charges and pore size distribution of the modified activated carbon model were studied by molecular dynamics and giant canonical Monte Carlo simulation, and the kinetic characteristics and adsorption mechanism of toluene in modified activated carbon were further analyzed. The results showed that the introduction of hydroxyl can improve the adsorption capacity of activated carbon to toluene, and hydroxyl content significantly affected the adsorption capacity. At high relative pressure, the best concentration of the hydroxyl group was 39.4%, and when hydroxyl concentration exceeded this value, the adsorption amount of toluene decreased. The strong electronegative oxygen atom in the hydroxyl group of modified activated carbon and the hydrogen atom in the methyl of toluene were combined to form a Lewis acid-base pair, which led to a stable adsorption structure and then increased the adsorption capacity of activated carbon to toluene. At low relative pressure, the main factors affecting the adsorption capacity were porosity and pore size. The modified activated carbon with hydroxyl content of 20.8% and 31.4% had massive micropores and a relatively compact structure, which was favorable for toluene adsorption. The self-diffusion coefficient of the toluene molecule in activated carbon was decreased by hydroxyl modification, and the diffusion coefficient was the lowest in activated carbon containing 39.4% hydroxyl. This was because the non-bond interaction between the toluene molecule and modified activated carbon hindered the movement of the toluene molecule. In addition, according to the variable-temperature adsorption research, the increase in temperature was not conducive to the adsorption of toluene by activated carbon since it was an exothermic process. This study can provide a theoretical basis for the improvement of the adsorption performance of activated carbon materials.