The issue of precise measurement of the infrared imaging temperature on a surface shielded by diffuse medium can be attributed to accurate calculation of the spectral bands optical depth of the medium at which the infrared image works. Infrared imagery temperature of the object shielded by the fine water sprays is taken as examples. A specific measurement method is presented by theoretical and experimental analysis. The geometrical parameters of diffuse medium (particle size, concentration, depth and so on) are measured by particle measuring system, the optical extinction coefficients combined with the theoretical calculation of Mie scattering are obtained, and the air transmissivity of the medium with Lambert-Beer law is calculated. Though setting the atmospheric transmission parameters in the infrared image, and complete the operation of accurate temperature measurement. Experimental results show that this method can accurately measure the surface temperature of the dispersion medium shield. As to the problem of the practical application, a method to estimate atmospheric transmissivity is proposed.