Abstract: In a vertical furnace for continuous hot-dip galvanizing of strip steel, zinc vapor forms zinc ash in the snout. A model of zinc vapor diffusion was developed to predict the movement characteristics of zinc vapor, and the model was verified by literature. On this basis, the zinc vapor concentration in the snout was compared for three structural improvement cases（baffle, exhaust devices and installation of both devices）, and the improvement effects were compared for different extraction flow rate. The results show that all three improvement conditions can effectively reduce the diffusion of zinc vapor in the annealing furnace. The simultaneous installation of baffles and extraction devices is the most effective case. With the increase of the extraction flow rate, the concentration of zinc vapor in the furnace tends to decrease at first and then stabilize gradually.The conclusions obtained in the paper can provide guidance on the diffusion trend of zinc vapor inside the vertical furnace and can quantitatively evaluate the effect after improving the structure of the snout area.