Abstract: L-type plasma melting furnace has a unique advantage in the treatment of low and medium level radioactive waste due to its high pyrolysis gasification efficiency and inhibition of nuclide volatilization. Due to the high temperature characteristics of the plasma torch in the furnace, there is a problem that the temperature is uncontrollable when the plasma torch is used in the heating stage, resulting in poor temperature distribution uniformity in the furnace and even damage or failure of local refractory materials in the furnace in serious cases. In this paper, a finite element numerical simulation model is established for an L-type plasma melting furnace, and the influence of hot air inlet distribution position and plasma torch installation position on the preheating effect in the furnace is investigated. The results show that if the air inlet is arranged symmetrically, a hot air hedge will be formed, and heat transfer in the furnace will be blocked. If the unilateral hot air inlet arrangement can avoid the low temperature zone at the corner of the upper shaft furnace and the lower furnace, the temperature difference in the furnace is not obvious in this way. Through the test comparison, the overall temperature distribution uniformity in the furnace is better when three unilateral air supply ports are opened, the total air inlet flow is 200 m³/h, the hot air temperature is 200℃, and the installation angle of the plasma torch (76 kW) is 40°. The conclusions of this paper can provide practical guidance for the design and operation of the L-type plasma high-temperature melting furnace and improve the reliability and safety of the equipment.