The authors have proposed a direct decomposition plant system for persistent waste oil by use of microwave-induced non-equilibrium plasma combustion. This study performed thermodynamic analysis of the proposed plant system as well as combustion experiments of the non-equilibrium plasma combustion. The combustion experiments showed that the low calorific value of exhaust gas from the combustion remarkably depended on oxygen ratio in the combustor, and the calorific value increased as the oxygen ratio decreased. The thermodynamic analysis revealed that the thermal efficiency and specific power of the proposed system were as high as 44.2% and 326.2 kJ/kg, respectively. These results suggested that the proposed system could supply all of the power required to operate the non-equilibrium plasma combustion.