The invention relates to an ultrathin film of a transparent high-strength and high-conductivity electrical self-supporting carbon nano-tube and a preparation method thereof. The ultrathin film mainly comprises a network consisting of interweaved carbon nano-tubes, and the application amount of the carbon nano-tubes is 0.01-0.7 mg/cm<2>; and the thickness of the film is more than 10nm, the light transmittance of the film is 50-97%, the electrical conductivity of the film is 30-500 MS/m, the tensile strength of the film can be as high as 2000MPa, and the ultrathin film has a larger area. The ultrathin film is prepared from single-walled and/or double-walled and/or multi-walled carbon nano-tubes through the steps of filtering, printing, coating and the like so as to form films, and then stripping from the formed films so as to from self-supporting films. The ultrathin film of the self-supporting carbon nano-tube provided by the invention has ultrahigh mechanical properties and excellent electronic and optical properties, therefore, the ultrathin film can be widely applied to the technical field of photoelectricity; and meanwhile, the ultrathin film is simple in process, easy to operate, good in controllability, safe and environmental-friendly, and can be prepared by using merchant carbon nano-tubes as raw materials, therefore, the ultrathin film is wide in material source and low in cost and is suitable for the industrial production on large-batch and large-area ultrathin film preparation.