Abstract: As the study and evaluation of the long distance infrared dim-small target detection algorithm requires a large amount of test images, a method of the IR dim-small target image simulation was proposed based on nonlinear mapping model. First, the irradiance and imaging gray value were got by theoretical calculation and actual shooting. By taking advantages of the data the various alternative mapping models so as to get the best mapping model were evaluated. Then, the mapping model was applied to the simulation process of actual target image and the target simulation image was got which reflected the real brightness variations. Finally, considering the effect of atmospheric transmission and so on, the target simulation image was combined with real background image to get final infrared dim-small simulation image. By comparison with the traditional simulation method, this proposed simulation method has more sense of reality.