Abstract: First, based on the aberration theory of the plane symmetric grating reflector system, the wave aberration of the imaging beam was corrected according to the optics material refractive index, and the aberration theory was extended to the plane symmetric refractive optical system, which made this theory can be applied to the aberration calculation of the catadioptric combined optical system with beam oblique incidence. Secondly, it was pointed out the computational expressions of wavefront aberration should be kept uniformed in view of the refractive index relationship between object and image spaces and the definition of direction of incident angle. Finally, the analysis and calculation were carried out on the aberration of the catadioptric ellipsoid mirror shape detection optical system by applying the extended aberration theory, and compared with the Zemax ray-tracing results to verify the effectiveness of the wave aberration theory. This aberration theory provides effective measures for the design of the catadioptric combined optical system with beam oblique incidence, the evaluation and optimization of image quality.