A method for making a thin film transistor, the method comprising the steps of: (a) providing a carbon nanotube array and an insulating substrate; (b) pulling out a carbon nanotube film from the carbon nanotube array by using a tool; (c) placing at least one carbon nanotube film on a surface of the insulating substrate, to form a carbon nanotube layer thereon; (d) forming a source electrode and a drain electrode; wherein the source electrode and the drain electrode being spaced therebetween, and electrically connected to the carbon nanotube layer; and (e) covering the carbon nanotube layer with an insulating layer, and a gate electrode being located on the insulating layer.