In this article we describe the linear zone plate monochromator of the beam line BL12A at HESYRL. The monochromator will provide a monochromatic SR light source for a soft X-ray scanning microscope. It consists of four chambers that contain its optical elements. Three kinds of condenser zone plates are used as its dispersing and focusing elements and a pinhole as its exit slit. Being moved over a distance of 220 mm along the optical axis, the zone plates cover the wavelength range from 20 Å to 54 Å. Then a microzone plate images the monochromatic light to an ultimate spot size of 0.2 μm in a diameter at the sample.