A carbon nanotube thin film transistor and a manufacturing method thereof are provided in the embodiments of the present disclosure. The carbon nanotube thin film transistor includes: a base substrate; a gate electrode, a semiconductor layer, a source electrode and a drain electrode, which are disposed on the base substrate, the semiconductor layer includes a poly(3-hexylthiophene) layer and a mixing layer of semiconducting carbon nanotube and poly(3-hexylthiophene) which are stacked. The semiconducting carbon nanotube thin film transistor has a high purity, thus the metallic carbon nanotubes are substantially cleared out and the electrical property of the thin film transistor is ensured, so that the manufactured carbon nanotube thin film transistor has good electrical properties.