In this chapter, the authors develop a direct current (DC) plasma appliance for the vitrification of fly ashes from both medical waste incinerator and municipal solid waste incinerator. The thermal plasma torch is an alternative and promising technology for vitrification of hazardous fly ash. The plasma torch consists of four major parts: cathode, first anode, linked part and second anode. The authors investigate the transformation of the mineralogical species of fly ashes and the leach ability of major heavy metals during melting process in order to ascertain the mechanism of fixing metal in molten slag. However, during incinerating municipal solid waste and medical waste, a great quantity of fly ashes from the air pollution control systems, which were set up for wiping off hazardous materials in the flue gas, were discharged. A lab-scale DC thermal plasma melting system was used to dispose the hazardous fly ashes.