A method for preparing a carbon nanotube (CNT) film is provided, comprising: providing a growth chamber of CNTs, which includes an inlet end, an outlet end, and a first-level growth cavity and a second-level growth cavity, and the first-level growth cavity and the second-level growth cavity are in fluid communication between the inlet end and the outlet end; making precursor materials, which are used for forming CNTs, react in at least the first-level growth cavity of the growth chamber of CNTs to generate CNTs; and making a carrier gas flow into the growth chamber through the inlet end, and pass through the first-level growth cavity and the second-level growth cavity in sequence, wherein, a radial dimension of the first-level growth cavity in a flowing direction of the carrier gas is smaller than that of the second-level growth cavity at a junction between the first-level growth cavity and the second-level growth cavity, and a bubble blowing process is conducted with the precursor materials under the drive of the carrier gas at a position of an opening of the first-level growth cavity within the second-level growth cavity to generate a closed cylindrical CNT film partially disposed in the first-level growth cavity. The method of the present invention can prepare continuous, ultrathin and self-supported transparent conductive CNT film continuously and directly.