KBA X-ray microscope is a grazing non-coaxial incident X-ray microscope. The front pair mirrors are not perpendicular to the back pair strictly, which brings much difficulty to the analysis of image quality. Thus general optical CAD program is not suitable to this kind of optical system. The co-axial spherical refrective vector formulations are adjusted to establish the program for the non-coaxial grazing incident microscope, with which the aberrations and the synthesis errors are analyzed. The analytical results show that KBA microscope is a large aberration system. For an object distance tolerance of -0.4～1 mm, the grazing angle tolerance is -8″～0″, the separation angle tolerance of two mirrors is -20″～0″, and the change of dispersion spot is in an allowed range. This program is meaningful for the analysis and fabrication of KBA microscope.