The vertical continuous annealing furnace plays a pivotal role in the annealing treatment line of strip steel. Within this furnace, expelling the air by blowing protection gas is essential. This helps reduce the oxygen content, thereby preventing the formation of oxides and impurities on the surface of the strip steel. This study aims to investigate the influence of the structure of the overaging section of a vertical continuous annealing furnace on the blowing effect. The gas flow characteristics during the blowing process have also been examined, revealing the location and distribution of stagnant zones. Computational fluid dynamics (CFD) is used to solve a three-dimensional (3D) simulation model numerically, calculating the flow and velocity of gas within the furnace for blow times ranging from 0 to 100 seconds. The results indicate that the flow field in the furnace reaches a quasi-steady state at a blow time of approximately 75 seconds. However, the issue of flow field voids and stagnant zones shows negligible improvement beyond this point. The blowing effect varies across different regions of the furnace, with a notable area of flow field void and stagnant zone in the lower part of the furnace, far from the furnace throat, resulting in a suboptimal blowing effect. The findings of this study can serve as valuable guidance for optimizing the internal structure of a vertical continuous annealing furnace and improving the efficiency of the blowing process.