Abstract: The change of boron content in liquid steel during production process BOF-LF-CC was tracking from plant trials. The loss mechanism of boron was discussed based on experimental results and thermodynamics. In addition, optimization measures were proposed. The results show that reactions between B and O, N, N₂cannot take place, the oxidation reaction between B and O₂ in the air is the main way to lose boron. Avoiding the B exposing to the air can be a effective method to reduce the loss of boron in liquid steel, therefore, three optimization measures have been put forward. (1) Preventing the oxidation reaction between the steel liquid and air by controlling the stirring power; (2)Lidding the steel ladle during the transportation process from refining furnace to tundish to avoid the liquid steel exposing to the air; (3)Enhancing the tightness between tundish and mould during the casting process.