Recycling of various wastes such as sewage sludge requires an energy conversion process like thermal pyrolysis/gasification. During the process, tar and syngas are produced, but the tar brings trouble in pipelines and creates operating problems for the facility. In this study, to investigate naphthalene destruction in a gliding arc plasma reformer, parametric experiments were achieved in the variables that can affect the destruction efficiency. And through the parametric studies, the optimal operating conditions and the results were taken. For the parametric studies, steam input amount (steam/carbon ratio), input discharged power SEI (specific energy input), total feed gas amount, input naphthalene concentration, and electrode length were selected for experiments. Optimal conditions were 2.5 of S/C ratio, 1 kWh/m3 of SEI, 18.4 L/min of total gas amount, 1% of input naphthalene concentration, and 95 mm of electrode length. The corresponding maximum destruction efficiency of naphthalene was 79%, and energy efficiency showed 47 g/kWh.