A falling liquid film (FLM) method for suppressing the vertical infrared of military targets under constant heat flux boundary conditions is analyzed in detail. A flow and heat transfer model of a laminar falling film is established. The temperature distribution on the falling film surface is obtained using the energy conservation method and omitting the liquid film inlet effect, which simplifies the solution process. By comparing the results of different studies, the effectiveness of the energy conservation method for evaluating the heat transfer process of a falling film in a fully developed section is verified. The recognition distance of the detector to the target is calculated using liquid film infrared suppression technology. The results show that increasing the flow rate and sufficiently controlling the inlet temperature of the liquid film enhances the infrared suppression effect on a specific target. The research methods and conclusions of this study have important applications in providing a point of reference for infrared suppression of military targets.