NOx are main toxic by-products in the effluent gas when decomposing volatile organic compounds in air by a packed-bed plasma reactor. Several types of materials such as 13X zeolite, BaTiO3 and Pd/Pt catalysts have been selected to be packed in the reactor, and methane decomposition and NOx by-products in discharged gases are investigated at different range of reaction temperature and discharge energy density at atmospheric pressure. The ratios of methane decomposition percentage/NOx concentration are used to assess these packed bed materials and reaction conditions. The results show that using Pd/gamma-Al2O3 with lower percentage Pd as packed bed, and discharging with lower discharge density at higher reaction temperature can reduce NOx output effectively and greatly improve performance of the reactor.