A carbon nanotube array includes a plurality of carbon nanotubes and at least one line mark formed on the carbon nanotubes. The carbon nanotubes have a top end and a bottom end. The at least one line mark is formed on the carbon nanotubes. The at least one line mark transversely extends across the carbon nanotubes, and is located between the top end and the bottom end. The at least one line mark is spaced from the top and bottom ends.