A method for fabricating a supermirror for forming a neutron guide. In the method, a neutron supermirror, which is widely used in the formation of thin films in cold neutron guides and the spectrometer field, is fabricated with nickel thin films and titanium thin films, having varying thickness, using a combination of monochromator structures in which nickel thin films and titanium thin films, having the same thickness, are stacked in the form of periodic structures. According to the method, a combination of monochromator structures having a variety of different thicknesses is formed, such that the amount of the overlap of peaks due to the monochromator structures can be adjusted to increase reflectivity, and some of the monochromator structures can be removed during the fabrication of the supermirror to make it easy to extract monochromatic beams, such that it is easy to fabricate a transmission monochromator, rather than a reflection monochromator.