Abstract: The analytical result of Fraunhofer-Diffraction of the circular ring is known but that of the similar circular ring isn't. Based on Kirchhoff diffraction integral formula, the analytical result of Frauhofer-Diffraction on the similar circular ring is derived in this paper. Utilizing the relations of curve coordinate and Fourier-transform of similar circle. The diffraction patterns of the several typical similar circular rings are given and analyzed.