Abstract: Based on the experimental data of ultra-low carbon aluminum killed steel in a 300 t ladle of RH treatment, a model for predicting the total quantitatively oxygen content of molten steel was established. Some factors such as treatment time, argon flow rate, molten steel circulation rate, snorkel diameter, FeO and MnO content in ladle slag were considered in the model. Potential improvements for RH operation were discussed. According to model analysis, the methods for promoting inclusion rising are increasing the argon flow and enlarging the snorkel diameter, but they have proper ranges.