The　precipitation　process　of　inclusions　in　the　high　sulfur　steel　with　the　cerium　addition　is　observed　using　the　high-temperature　confocal　scanning　laser　microscope　(CSLM).　Rare　earth　(Re)　inclusions　formed　in　the　molten　steel,　and　MnS　inclusions　precipitate　along　grain　boundaries　or　on　oxide　cores　at　the　end　of　solidification.　With　the　addition　of　cerium,　the　average　aspect　ratio　of　inclusions　in　the　steel　decreases　from　6.5　to　5.0,　and　the　addition　of　cerium　effectively　modifies　the　elongated　MnS.　Thermodynamic　calculations　show　the　inclusion　transformation　during　solidification,　yet　it　lacked　the　formation　of　Ce2O2S　and　Re　sulfides.　According　to　the　first-principles　calculation,　the　priority　of　the　inclusion　formation　was　Ce2O3　＞　CeAlO3,　Ce2O2S　＞　CeS　＞　Ce3S4　＞　MnS.　The　stability　of　MnS　inclusions　is　much　lower　than　that　of　cerium-containing　inclusions.　It　is　in　situ　observed　that　the　addition　of　cerium　promotes　the　formation　of　cerium-containing　inclusions　and　reduces　the　precipitation　of　MnS　in　the　high　sulfur　steel.