A novel double-tube dielectric barrier discharge (DDBD) reactor was established by us to degrade styrene. The DDBD reactor contains two discharge zones with one power supply, the outer tube zone with low discharge energy and the inner tube zone with high discharge energy. The gas first flows into the outer tube zone and then flows into the inner tube zone, at last flows out from the inner tube zone. Compared with traditional single-tube dielectric barrier discharge (SDBD) reactor, the DDBD reactor shows the following advantages: (a) the energy utilization efficiency can be improved because the low bond energy groups in styrene can be destroyed first in outer discharge zone by weak discharge energy and the high bond energy groups such as aromatic rings can then be concentrated destroyed in inner discharge zone by high discharge energy; (b) the high mineralization efficiency results in no oil-like byproducts aggregated on the surface of reactor surface; (c) the double dielectric layers are protected from penetration. The diameters of outer and inner tubes were optimized and the DDBD reactor with 25 mm outer tube and 6 mm inner tube exhibited the best styrene mineralization efficiency. Compared with SDBD reactor with the same outer tube diameter, the selectivities of CO and CO2 were improved by 40% with the styrene concentration of 2000 mg m(-3) at the applied voltage of 11 kV. Meanwhile there was no any oil-like byproducts observed aggregated on outer tube wall, inner tube outlet and the electrode after 6 h treatment. The applied voltage, oxygen content, discharge length and relative humidity were optimized in this research and the byproducts of O-3 and NOx were also detected and discussed. (C) 2014 Elsevier B.V. All rights reserved.