When the model of infrared attenuation of water mist is established, the space of water mist is usually treated as a homogeneous whole. However, because of diffusion, the droplet density of water mist can not be kept consistent everywhere. So there is commonly a great deviation between the simulation result and the actual situation. To solve this problem, a new modeling method based on Gaussian diffusion theory and Mie scattering theory is proposed. By dividing the space of water mist into several subspaces and calculating the extinction performance of the water mist in each subspace, the modeling accuracy is improved. At the same time, the infrared radiation attenuation of the water mist in different directions is analyzed according to the simulation result. This research work is of a certain reference value to the making of an effective infrared countermeasure strategy.