Abstract: The composition of inclusions in low melting point area of CaO-SiO₂-Al₂O₃-MgO system and CaO-SiO₂-Al₂O₃-MnO system was analyzed by thermodynamic calculation,and the influence of Al₂O₃ content on inclusions in steel was studied. It is found that,at the Al₂O₃ content of 15wt%,the corresponding low melting point area of phase diagram takes the largest percentage. The angular Al₂O₃ inclusions increase by the increase of Al₂O₃ content,and the distribution of inclusions in steel becomes relatively concentrated.In the basicity of 1.2 and the Al₂O₃ content of 8wt%,the inclusions can be controlled in low melting point area of phase diagram,the corresponding shape of inclusions is spherical with the size of about 5 μm.