The model of line-by-line integration has the greatest accuracy in atmosphere absorption transmittance calculation,but its poor realtime property limits its application in engineering. A model of atmosphere absorption transmittance with spectral resolution of 1 cm-1 is given for IR scene real-time engineering simulation,and it can meet the demands of realtime and accuracy. Firstly,the gas transmittance of 1 cm-1 band with constant temperature,pressure,gas density and different distance is calculated by line-by-line integration,and the models of absorption transmittance and altitude are built. The gas absorption transmittance on random route is calculated by interpolation finally. The results show that the accuracy of the atmosphere absorption transmittance calculated by the model is better than that of MODTRAN,and the calculation speed of the model is much faster than that of line-by-line integration.