By taking advantage of the rotational symmetry, the electromagnetic characteristic of the body of revolution (BOR) radome is fast analyzed by the method of moments (MoM) based on the mode decomposition technique. First, the MoM matrix equation governed by the surface integral is established and the theoretical model is reduced in dimension by using the mode decomposition technique in view of the object's structure characteristic. Then, the integrals in the mode decomposition of the incident field are replaced by the fast Fourier transform (FFT), thus the decomposition coefficients of all modes on a given annulus can be fast and easily obtained through one FFT. Due to the surface equivalent electric and magnetic currents gotten by solving the matrix equations having the form of superposition of mode components, the analytical approach is used to substitute for the integral in the calculation of the far field pattern, so the computing time is greatly reduced. Examples are presented to demonstrate the accuracy and efficiency of the proposed method in this paper.