Abstract: The modulation transfer function(MTF) can objectively evaluate the imaging performance of optical system. Based on the theory of wave aberration of plane symmetric optical system, the wave aberration expression of main aberration of Kirkpatrick-Baez(KB) microscope optical system was given. By using the autocorrelation method, the MTF curve of the KB system was obtained by the Gauss-Legendre numerical integration, and then compared with the MTF curve of the optical analysis software. The results show that calculating the MTF by wave aberration theory can not only quantificationally and intuitively analyze the imaging performance of KB system, but further analyze the single aberration distribution of optical system. The application of this theory can provide a more effective targeted optimization scheme for KB system.