The Lead-cooled Fast Reactor (LFR), as a significant approach for the sustainable development of energy in the future, requires controlling the oxygen concentration within an appropriate range to effectively regulate the corrosion rate of metal elements in the LFR. In this paper, numerical computations of the oxygen concentration distribution under diverse control measures are conducted using Computational Fluid Dynamics (CFD) software, the transport process of oxygen in liquid bismuth is simulated through the component transport model, and a comparative analysis of the two gaseous control methods, ON_OFF and PID, is accomplished based on the secondary development of the User-Defined Function (UDF). The findings indicate that natural convection serves as the dominant driving force for oxygen transport within the natural circulation system. The diffusion coefficient of oxygen in lead–bismuth has less influence on oxygen transport. The PID oxygen concentration control is more stable when compared with the ON_OFF control. This study can furnish a reference for both experimental and engineering designs.