The invention provides a preparation method of an array carbon nanotube thin film. The method includes the following steps: placing a base in a metal mesh enclosure inside the cavity of a PECVD device and placing two orderly stacked catalytic metal plates on the metal mesh enclosure; introducing reaction gas into the cavity of the PECVD device, performing heating, switching on the power, performing a reaction and acquiring a catalytic thin film on the surface of the base; and heating the cavity of the PECVD device, introducing carbon sources and carrier gas, switching on the power, performing a reaction and acquiring the array carbon nanotube thin film on the surface of the base. According to the invention, the preparation of the catalytic thin film and the array carbon nanotube thin film are finished in the same cavity of the PECVD device and continuous preparation can be realized so as to increase the preparation efficiency of the array carbon nanotube thin film; and on the other hand, low-temperature preparation enables the array carbon nanotube thin film to be applied to a plurality of fields which are not resistant to high temperatures.