Based on the similar kinetic mechanism, the vacuum degassing process of molten steel is simulated by using the release process of dissolved oxygen (DO) in water. Under the condition of vacuum pressure experiment, it was found that a large number of small bubbles would be precipitated from the vessel internal wall or the surface of oxygen probe, which was very similar to the internal degassing reaction site assumed by previous degassing mathematical models. To verify the existence of internal degassing sites, the mechanical stirring was introduced to analyze and calculate the degassing rate at the bath surface and internal site.The results showed that the degassing rate of bath surface was very low in the whole process, and the bubbles precipitated from the internal degassing sites would greatly improve the DO removal rate, especially when the pressure P=25 kPa, its degassing rate was about 10 times of that at the bath surface; It was also confirmed that the internal degassing reaction mainly occurred in the initial stage of degassing, that is, in the range of high DO concentration. Besides, the removal of dissolved oxygen is also a first-order reaction process, and its volumetric mass transfer coefficient kA/V is constant. Therefore, the DO removal process can be used to simulate the degassing behavior of molten steel. In order to describe the effect of vacuum pressure and argon flow rate on kA/V, the function relationship between log(kA/V) and logε was obtained by introducing the concept of stirring power density ε, which was compared with previous simulation studies.