To facilitate ultra-high resolution spectroscopy measurements on sub-micron size single crystals, we have designed a Dragon-type soft-x-ray beamline that can achieve an energy resolving power greater than 50,000 for 400-1200 eV photon energies using a non-movable exit-slit scheme and a varied-line-space active grating of 1200/600 l/mm ruling density. The resolving power is higher than 50,000 and the photon flux is greater than 1×1011 photons/sec for 700-800 eV photon energy ranges in which most photoelectron experiments will be carried out. Two KB mirror sets, each containing a horizontal and a vertical mirror, are placed before and after the grating separately, to pre- and re-focus the undulator effective size of 240 μm in horizontal and 20 μm in vertical down to sub-microns scale at the sample position. Among these KB mirrors, two horizontal ones are arranged in a two-stage demagnification scheme (0.192 × 0.019) and also avail to control the horizontal beam size with a slit at the first horizontal focal point. With this slit wide open, the beam size at the sample position is 1.2 μm in horizontal and 0.4 μm in vertical, assuming a 1 μm opening for the grating monochromator exit slit. A sub-μm horizontal beam size can be obtained by closing down the horizontal opening of the slit at the first horizontal focal point.