The invention provides a low-refractivity waveguide modulator for graphene. The low-refractivity waveguide modulator comprises a substrate, lower cladding, a waveguide core layer, an ITO transparent electrode, a lower insulating medium layer, a single-layer graphene film, a metal electrode, an upper insulating medium layer and a high refractive index silicon oxide layer, wherein the lower cladding is arranged on the substrate, the waveguide core layer is arranged in the middle of the lower cladding for forming a ridge-shaped structure, the ITO transparent electrode is arranged on the waveguide core layer and the two sides and covers the exposed upper surface of the lower cladding, the lower insulating medium layer is arranged on the surface of the ITO transparent electrode, the portion, on one side of the ridge-shaped structure, of the insulating medium layer is of a disconnection shape and forms a window, the single-layer graphene film is arranged on the lower insulating medium layer, the metal electrode is arranged on one side of the ridge-shaped structure and the single-layer graphene film of the other side far away from the window, the preset distance larger than 800nm is kept between the metal electrode and the ridge-shaped structure, the upper insulating layer is arranged on the single-layer graphene film on the ridge-shaped structure, and the high refractive index silicon oxide layer is arranged on the upper insulating medium layer. The low-refractivity waveguide modulator has the advantages of being small in size, wide in modulation bandwidth, low in insertion loss and simple in preparing process.