The invention discloses a preparation method for a carbon-based thin-film attenuation filter, relating to a filter. The invention provides a preparation method for a carbon-based thin-film attenuation filter which is simple in technology, easy in the design of a film system, and good in stability. The preparation method comprises the steps of cleaning a substrate; by taking graphite as a target material, performing vacuum film plating on the substrate through using a plasma beam sputtering method to obtain the carbon-based thin-film attenuation filter. The prepared carbon-based thin-film attenuation filter is simple in film system, good in stability and simple in preparation technology. The adhesive force of a carbon-based thin film and the substrate is high. The carbon film has smooth attenuation within visible wavelength range, and lower reflectivity is guaranteed so as to inhibit stray light; the carbon film has higher attenuation within in near ultraviolet, and can partially replace functions of a UV mirror to protect an inductive element. The thickness of the carbon-based thin film can be realized through controlling the function of a radio-frequency coil, the bias voltage of the target material, and the sputtering deposition time.