Based on theory of infrared detection,the process of infrared image simulation is analysized in this paper.It is pointed out that the present simulation methods only take into account the effects of radiant energy distribution and view field partition of infrared detector pixel.Whereas the diffraction effec of optical system on infrared radiation signal is neglected,which results in very clear boundaries in simulated infrared image.In order to simulate the some what blurred boundary in real infrared images,Gaussian point spread function is used to convolve the simulated infrared image.By this way,the similitude between the simulated images and real infrared images is improved significantly.