Abstract: A manufacturing method of forming undertone layer of optical fiber with single-layer coating is provided. The optical fiber with single-layer coating includes, from the center outwards, glass core, cladding layer (outer diameter 80 um-125 um) and permanent coating (thickness 4 um-8 um). The method of forming undertone layer over permanent coating includes: placing optical fiber in a coloring machine so that coloring machine guiding optical fiber moving forwards, coloring machine having at least a mask device and a UV curing device; coating an undertone layer on permanent coating of optical fiber when optical fiber passing mask device, the thickness of undertone layer being 3-200 um; irradiating UV onto optical fiber passing UV curing device to solidify the undertone layer on permanent layer; and coloring machine collecting processed optical fiber, the coating strip force of undertone layer of optical fiber being less than 1 Newton.