Abstract: The Fraunhofer diffraction phenomenon on the complementary structure of Sierpinski carpet grating is discussed on the basis of FresnelKirchhoff theory and Fourier analytical method. The frequency spectrum,amplitude and lightintensity functions are derived. The diffraction phenomenon of grating is simulated by use of the MATLAB software, and the curves of its frequency response characteristic are plotted. The result shows that in diffraction patterns of allorder gratings, the higher amplitude part is concentrated in the center area of the receiving screen and the lower amplitude in the area around the center, but in the further area far away from center it tends to 0. In the whole, the diffraction patterns manifest the obvious fractal characteristics as well as the basic features of the diffraction.