As a main composition of dye wastewater, organic pollutant which has a negative effect on the environment can be effectively removed by active carbon adsorption. In the present work, activated carbon fiber (ACF) was modified by a novel modification technology, gilding arc discharge, while its adsorption capacity was studied with the acid orange II (AO II) solution selected as the target wastewater. Several factors, such as air flow rate, distance between samples and the discharge area, pH of the solution and plasma treating time, were investigated with respect to their effects on properties of the plasma-treated ACF, in terms of texture characteristic, surface chemical compositions and adsorption capacities. The results showed that the specific surface area and pore volume of ACF decreased after the plasma treatment, while the amounts of oxygen-containing functional groups on the surface of ACF increased compared with the raw ACF. Moreover, it was observed that the adsorption capacity of the modified ACF was improved by nearly 20.9 %, which was beneficial to the industrial application.