To improve the output image contrast of infrared scene simulation system based on digital micro-mirror device(DMD),the configuration and work principle of DMD are analyzed, the model is set up with its configuration characteristics similarity as blazing grating． The diffractive characteristics of DMD is analyzed with the theory of Fourier optics and simulated with MATLAB． As monochrome parallel light incidence, the distribution variety of diffractive light intensity is analyzed by changing the wavelength, it is found that the diffraction effect gets evident when the wavelength of incidence light is close to the size of micro-mirror． The distribution variety of diffractive light intensity is analyzed by changing the incidence angle, it is found that the diffraction light intensity changes, and it has an effect on the output image contrast． The output image contrast can be improved by changing the incidence angle of the light source in the infrared scene simulation system．