The reason of blast furnace slag pulverization is analyzed: calcium oxide in limestone and silicon dioxide in ore combine to form dicalcium silicate and tricalcium silicate to form slag, which has dephosphorization function. When the blast furnace is tapping, the slag is discharged together, and the slag floating on the upper layer is discharged into the slag flushing pool through the separator to form blast furnace slag, which can be used as cement raw materials or superfine powder building materials. The special slag outlet of blast furnace regularly discharges the slag directly into the slag flushing pool. In the accident state of slag flushing pool and slag discharge ditch, sometimes slag is discharged into the reserved dry slag pit to form dry slag of blast furnace.