To improve the energy efficiency in dye degradation, a circulatory airtight reactor system was developed. Experiments were conducted to estimate the effects of various parameters on the degradation of methyl orange (MO). It was found that MO degradation depended on the initial concentration and total volume of the compound, being slower for higher concentrations and larger volumes. There existed a maximal MO decoloration efficiency with the change of oxygen velocity. This reactor had better performance of the conductivity resistance on MO degradation. Relatively high or low pH of the solution was adverse for MO removal. After 20 min plasma treatment, 92% removal of MO was achieved and the corresponding energy efficiency was 11.68 g/kW h with gas velocity of 0.08 m(3)/h and the input energy of 5.67 W. Besides, compared with three other reactor systems, this gas discharge reactor system expressed prominent energy efficiency and supreme reaction rate constant. Lastly, bond dissociation energies (BDEs) theory was applied to propose the degradation mechanism of MO. (C) 2012 Elsevier B.V. All rights reserved.