An emitter includes an electrode, and a number of carbon nanotubes fixed on the electrode. The carbon nanotubes each have a first end and a second end. The first end is electrically connected to the substrate and the second end has a needle-shaped tip. Two second ends of carbon nanotubes have a larger distance therebetween than that of the first ends thereof, which is advantageous for a better screening affection. Moreover, the needle-shaped tip of the second ends of the carbon nanotube has a lower size and higher aspect ratio than the conventional carbon nanotube, which, therefore, is attributed to bear a larger emission current.