Abstract: The effect of strongly reduced refining slag with different basicities and Al₂O₃ contents on non-metallic inclusions in molten steel was investigated through the slag-metal equilibrium at 1 600℃.When the slag-metal equilibrium is reached,the mass ratio of CaO to SiO₂ in refining slag is from 1.9 to 4.5,and the mass fraction of Al₂O₃ is from 21% to 33%.Non-metallic inclusions in steel are mainly the spherical CaO-MgO-Al₂O₃-SiO₂ system with size smaller than 5 μm.The composition of refining slag has a great effect on inclusions.Inclusions mainly distribute in the low melting point region of the CaO-MgO-Al₂O₃-SiO₂ quasi-ternary phase diagram with stable content of SiO₂ between 1 400℃ and 1 500℃.With the basicity of refining slag increasing and the Al₂O₃ content decreasing,part of inclusions gradually deviate from the low melting point region and the total number of inclusions decreases.When the mass fraction of Al₂O₃ is 21.22% and the basicity of refining slag is 3.27,lots of inclusions distribute in the high melting point region and the total number of inclusions is the smallest.