A method for making an array of carbon nanotubes includes the steps of: (a) providing a substrate with a film of a first catalyst thereon; (b) disposing the substrate in a quartz boat; (c) disposing a second catalyst adjacent to the substrate in the quartz boat; (d) disposing the quartz boat in a reaction chamber having a gas inlet configured for introducing a carbon source gas and a carrier gas into the reaction chamber and a gas outlet; (e) heating the reaction chamber to a predetermined temperature and introducing the carbon source gas into the reaction chamber along a direction from the second catalyst to the substrate, whereby the second catalyst reacts with the carbon source gas thereby producing a resultant for promoting catalytic activity of the first catalyst; and (f) growing an array of carbon nanotubes on the substrate.