In order to guide the practical application of lead-bismuth alloy (LBE) bubble lift pump, the dynamic characteristics of nitrogen bubbles with different diameters in liquid Lead-bismuth alloy (LBE) were studied based on the Volume of Fluid (VOF) model, and the changes of bubbles’ morphology and velocity during the movement were analyzed. The results show that the smaller the radius of the bubble is, the more drastic the change of its initial velocity and the smaller its maximum velocity are. For the small bubble, there is no bubble shedding in the process of its movement, only when the radius of the bubble reaches a certain value, the phenomenon of small bubble shedding will occur.