Abstract: The mechanism of precipitation and growth of Al2O3-TiN compound inclusions during IF steel solidification process was researched by experiments and theoretical analysis. The results showed that when the solid fraction exceeds 0.9, Al2O3 and TiN precipitate successively by heterogeneous nucleation and Al2O3-TiN compound inclusions are formed. The final diameter of compound inclusions increases with the decrease of cooling rate. When the cooling rate is constant, the growing extent of compound inclusions decreases with the increase of the radius of inclusions used for nucleus. The growing extent of TiN inclusions formed outside the Al2O3-TiN compound inclusions increases with the decrease of the radius of Al2O3 inclusions inside.