The adsorption properties of gliding arc discharge (GAD) plasma-modified granular activated carbon (AC) were studied with Pb2+, Fe2+, Ni2+, and Cu2+ solutions selected as components of the target wastewater. The physical and chemical properties of the surface of modified AC were monitored by scanning electron microscopy, elemental analysis, and automatic surface area and pore size analysis. The adsorbance of metal ions was measured by inductively coupled plasma optical emission spectrometry. The adsorbance of Fe2+ and Pb2+ increased with GAD modification time, whereas the adsorbance of Ni2+ and Cu2+ barely changed over time. The optimum modification time and gas flow rate were found to be 30 min and 0.9 L/min, respectively. The adsorption mode of Pb2+ or Fe2+ by AC with a modification time of 30 mm was monolayer adsorption. The adsorption kinetics of Fe2+ and Pb2+ on AC can be better described by a pseudo-first-order kinetic model.