The phenomena of oxygen contamination from crucible materials on molten steel during vacuum melting has been studied by a 50 kg vacuum induction furnace with magnesia crucible and a 25 kg vacuum induction furnace with calcia crucible to reseach the basic law and main factors of oxygen contamination from crucible materials on molten steel. TTie results showed that avoiding oxygen contamination from crucible materials on molten steel during vacuum induction melting was key factor for deep deoxidization of molten steel in extra-low oxygen content range; in 0

5 ~ 10 Pa vacuum melting

with vacuum and temperature of molten steel in bath increasing the oxygen contamination from crucible materials on molten steel increased

and the final oxygen content in steel increased with carbon burning loss of molten steel increasing; the oxygen contamination of molten steel melting with magnesia crucible was more than that with calcia crucible.