A thin film transistor including: an insulating substrate; a gate electrode, located on the insulating substrate; a gate insulating layer, located on the gate electrode; a carbon nanotube structure, located on the gate insulating layer; wherein the carbon nanotube structure includes at least one carbon nanotube, the carbon nanotube includes two metallic carbon nanotube segments and one semiconducting carbon nanotube segment between the two metallic carbon nanotube segments, one of the metallic carbon nanotube segments is used as a source electrode, the other one of the metallic carbon nanotube segments is used as a drain electrode, the semiconducting carbon nanotube segment is used as a channel.