Considering the issue caused by the tail gas of viscous oil fire flooding, which carries a large amount of jeopardizing liquid, the Liaohe Oilfield No. 56 desulfurization station applies the vertical processing separator as the main dehumidification equipment for moisture elimination. However, the lack of study on the separator’s gas–liquid separation mechanism leads to unclear recognition of the equipment’s processing capability, which easily causes the desulfurization tower to water out, and the tail gas gathering network system to get frozen and blocked. To result in a solution to the problems above, numerical simulation software is applied in this paper based on the oil field’s actual operation data to establish a mathematical model for calculation, which may assist in simulating the gas–liquid separating process, in analyzing the flow field distribution within the separator, and in studying the dehumidification mechanism in terms of influencing factors and laws of equipment dehumidification efficiency. Finally, this helps optimizing the separator’s structure based on the calculation results. The research results provide a theoretical basis and technical support for the practical application of dehumidification equipment in oil fields.