Abstract: By the method of using a full-process system sampling, a systematic analysis and research on the evolution of the oxygen content and the inclusion characteristics in a 20CrMnTi gear steel produced in the process of 120 t BOF-LF- VD-CC have been carried out. The experimental results show that using the technology of aluminum deoxidation and the high-basicity [ (CaO)/(SiO₂) =3. 8 ~7 ] reduction slag, the T[O] in the slab can be less than 20 x 10^-6 ； the average T[O] of liquid in tundish gas increases by 6 x 10^-6 ； during the steelmaking process of gear steel, the inclusions in steel have completed the transformation from Al₂O₃→ Al₂O₃ -MgO—;Al₂O₃ -CaO-MgO.