Activated carbon's porous nature and high specific surface area make it an effective tool for adsobing waste gas containing styrene. However, the mechanism by which oxygen-containing functional groups adsorb weak-polar styrene remains unclear. This study described the preparation of the modified activated carbon materials AC-S and AC-N using the acid leaching method. The pore structure and specific surface area of modified activated carbon, the evolution of oxygen-containing functional groups, and their impact on the styrene-adsorbing performance were investigated. The results demonstrated that acid modification significantly improved the styrene-adsorbing capacity of activated carbon. Physical and chemical adsorption impacted both modified and unmodified activated carbon materials, as determined by the adsorption kinetics studies and isotherm fitting analyses. Monolayer adsorption was more likely to occur on modified activated carbon. HNO₃-modified activated carbon (AC-N) maintained its effective styrene adsorption pore size range. The increasing number of oxygen-containing functional groups on the surface improved the styrene adsorption performance of AC-N. Study of oxygen-containing functional groups on the surface revealed that lactone group was a key factor in improving the modified activated carbon's ability to adsorb styrene. Density functional theory (DFT) calculations showed that lactone group on AC-N strongly interacted with the vinyl group in styrene, thereby enhancing the styrene adsorption performance of modified activated carbon.