An on-line converter back alloy baking system and device applied in metallurgical field. In the process of smelting steel, an alloy is needed to be added into molten steel. In order to effectively remove the free water on the alloy surface, reduce the crystalline water inside the alloy, reduce the formation of the hydrogen gas hole of the steel, so as to raise the mechanical properties of the product. reduce the tapping temperature, shorten the slagging time, reduce the consumption of slag making and increase the age of the furnace effectively, an on-line converter back alloy baking system and device are designed, which include the single on-line alloy furnace, the sealing mechanism of the heating turn plate valve, the position inspection device of the solid material, the alloy heating fire-proof furnace body and its anti-off fire mechanism, bottom cones of on-line alloy heating furnaces, and ect. By implementing the technical scheme proposed by this invention, the temperature loss of the alloy is small, the heating time is short, the structure is simple, the heating temperature of the alloy is high, reducing the temperature of the tapping is obvious and the age of the furnace can be increased effectively, so the enterprise can save a lot of cost, reduce the energy consumption and thus achieve energy saving and emission reduction, and the double effect of improving the quality of the product.