A Schwarzschild microscope with a numerical aperture of 0.2 and a magnification of 130 in a 100 μm field of view (FOV) is designed and is working at 13.5 nm. Meanwhile, a CCD is used as a detector with a pixel size of 13 μm × 13 μm and imaging area of 13 mm × 13 mm. The imaging quality with tolerances of system and errors of mirrors are considered. We obtain that the best on-axes object resolution can be up to about 200 nm, the average value is 230 nm, and the resolution is about 360 nm at 80 μm FOV.