As an important secondary refining reaction, RH is good at degassing and decarburizing. In the past 40 years, many researchers developed many mathematical models to investigate the fluid flow and the decarburization in RH, but the effect of CO bubbles on the fluid flow is not considered because of the complicated mathematical model and the heavy computing load. In this paper, numerical results show that the numerical result predicted by the two-way coupling model is closer to the experimental data than that by the one-way coupling model. During the decarburization, CO mole number, which is produced by decarburization reaction, is about 3 times argon mole number blown into the up snorkel. And the CO generation rate is greater than argon blowing rate at the first 9 min. Therefore, the fluid flow in RH can be described correctly only on the condition of considering both CO bubbles and argon bubbles, and the two-way coupling model is the necessary model to have a deep insight into the metallurgical phenomena in RH vessel.