Frequency resolution is a main parameter of the acousto-optic spectru m analyzer.Because the actual diffraction width of the acousto-optic Bragg device is much larger t han the theoretical width, we need to estimate the frequency resolution of the acousto-optic spectrum anal yzer by the actual diffraction width.Under the existing optical experimental platform,we establis h the mathematical model by the Gaussian function for the diffraction,which is stimulated by one radio frequency (RF) signal.We have solved the two Gaussian function superposition equations by dichotomy,and get th e minimum distance which could be distinguished under the Rayleigh criterion condition.According t o diffraction deflection distance of the optical system and the corresponding frequency bandwidth,we get the estimated frequency resolution.According to the multiplication property of Fourier transf orm,we generated the dual-frequency immediate frequency (IF) signal by the signal generator,and meas ure the frequency resolution of this optical system.The test results show that the estimated frequency resolution and the re al frequency resolution of this optic system are basically the same.We can estimate the acousto-optic f requency resolution by this method.