This paper analyzed the restricted link for cleanness of 20Mn2 steel which produced by BOF → LF→round billet CC process; the results show that reoxidation during the steel refining was the main restricted link for 20Mn2 steel cleanliness in Fengbao steel work. Reoxidation mainly occurred in three locations: first was after feeding the Si-Ca line; second was the process between LF end and tundish start; third was the casting process from the tundish to mold; The nitrogen and oxygen increased by 40×10^-6 and 109 × 10^-6 respectively from the LF start to CC process; the total removal mount of inclusions reached 198 × 10^-6. The content of large inclusions after feeding Si-Ca line and tundish increased significantly; and the typical reoxidation production manly was the Al-Si-Mn-Ti complex oxides. Therefore, the key measures for improving the steel cleanness were to make sure a good protective casting.