According to infrared smokescreens shielding principle, a model of infrared smokescreen transmittance in 3D space was constructed by using the extinction model and expanding model of infrared smokescreen.Considering the limitations of the traditional simulation method for the shielding effect of smoke screen, a method for simulating the transmittance in 3D space was proposed, and simulation was made for the method.The result of research indicated that the images of target observed by the detector is the result of stacking of several layers of transmittance, and the shielding effect is better than that of traditional methods.The method is of great significance for engineering application.