By means of Oxygen and Nitrogen Analyzer， Metallographic Examination， SLIME， SEM， EDS， etc.， the cleanliness of low carbon steel slabs（first slab， normal slab and final slab） produced in different casting stages by LD-argon-blowing station-CC. Through the comparative analysis of T［O］ and［N］ of different casting stages' slabs， the reoxidation of liquid steel was very serious in casting starting. However， it was not in casting ending. In comparison with the micro-inclusions' quantity of normal slab（7.96 per square millimeter）， the first slab and the fi- nal slab respectively increased by 98% and 33%. The component of micro-inclusions were mainly Al ₂ O ₃ and Al ^₂ O ₃ - （Mn， Fe）S. The quantity of large-inclusions was minimal， which was 1.91 mg/（10 kg） in normal slab. While the first slab contained the maximal quantity， it was 8.24 mg/（10 kg）. The quantity of large-inclusions was 2.72 kg/ （10 kg） in the end slab. Most of large-inclusions contained K or Na elements in the first slab and final slab， which might relate to serious slag entrapment in the mould when the casting starting and ending. The quantity of MgO- Al ₂ O ₃ inclusions and Al ₂ O ₃ -CaO-SiO ₂ -MgO inclusions was very high in the end slab， which suggested the entrap- ment in the tundish happened in the casting ending.