A design method integrating the aberration-corrected concave holographic grating and focusing mirror has been proposed, and the effect of the aberration of the optical source focusing mirror on the resolution and signal to noise ratio of the spectrometer is considered. A physical model of aberration analysis including a focusing mirror and a concave holographic grating has been built, an aberration coefficient expression is derived, a corrected aberration objective function is constructed, and an optimized design is finally obtained. In the integrated design, aiming at the monochromator grating in which the arm length is 170.3 mm and the curvature radius of the basement is 170.2 mm, the off-axis aberration caused by the focusing mirror is compensated through reversely increasing the holographic grating astigmatism. Compared with that of the traditional design, the root mean square size of image spot diagram decreases from 86 μm to 81 μm in the meridional direction, and from 765 μm to 167 μm in the sagittal direction. This method improves the capability of correcting system aberration and provides new design concepts for the optical system of concave grating spectrometers.