Abstract: During galvanizing process, zinc vapor oxidizes and forms zinc ash in a snout easily. The moving steel strip drives the protective gas and causes the drift of zinc ash. Coating defects may be caused by the ash, which sticks on the strip surface. Because the snout connects to the annealing furnace and the zinc pot, the ash may flow back to the annealing furnace. The ash hence pollutes the atmosphere in the snout. Therefore, it must be controlled or moved effectively. In this paper, an external circulation filtration procedure for the gas containing zinc ash was considered as an auxiliary device for an industrial strip product line. Numerical study of the flow in the snout was performed to assist the setup of the circulation device for the protective gas. The flow-rates of gas returning back to the furnace were calculated by the computational fluid dynamic method, and the zones where returning flow occured were visualized. In addition, the minimum circulation flow rates for non-returning gas were obtained by numerical orthogonal tests. Then under the minimum circulation flow rates, the flow in the snout was analyzed. Moreover, the details of returning flow zones were presented by a series of sections along the snout. With the aim of increasing humidity, nitrogen mixed with a slight part of water vapor (4% in volume) was used. Simulation results indicate that the humid nitrogen is suppressed by the returning flow and not able to humidify the atmosphere in the snout because of the guiding baffle. To improve the inflow path of humid nitrogen so that it can increase the contact between the surface and zinc liquid, a new inflow configuration using elbow-shaped tube was proposed, and its effects on improving the flow were validated. The results of the study provide a technical support for the setup of the circulation devices.