Aqueous Film Forming Foam (AFFF) fire extinguisher is the most effective firefighting system for large scale oil fire on big warship deck. The heat resistance effect is one of the primary extinguishing mechanism of AFFF as the extinguishing agent. When the AFFF film layer is formed on the surface of fire, its spreading effect will continually feed AFFF from outside; and due to the heat radiation of the fire, AFFF continues to ablate inside. The presence of the ablation process makes AFFF thinner, the thermal resistance capacity will decrease. When the fuel under the AFFF reaches a flash point, the fuel may be re-ignited, due to the air inside of the AFFF. To improve the AFFF extinguishing efficacy, a quantitative analysis of the flame retardant properties of AFFF and the distribution of the temperature field in the AFFF thermal invironment is of great significance. In this paper, a solid-state ablation model is proposed, and, based on this model, a steady-state ablation model of AFFF is established, combinating the ablation characteristics of AFFF and some assumptions, concerning AFFF density, ablation rate and the components rate of model. The temperature distribution within AFFF can be obtained through simulations. The result of simulation is lower than the experimental result, with an error of within 10%. The model can be used to calculate the AFFF flux for oil fire per area on the warship deck.