A method for distinguishing carbon nanotubes comprising: providing a conductive substrate and applying an insulating layer on the conductive substrate; forming a carbon nanotube structure on a surface of the insulating layer, the carbon nanotube structure includes at least one carbon nanotube; placing the carbon nanotube structure under a scanning electron microscope, adjusting the scanning electron microscope with an accelerating voltage ranging from 5˜20 KV, a dwelling time ranging 6˜20 microseconds and a magnification ranging from 10000˜100000 times; taking photos of the carbon nanotube structure with the scanning electron microscope; and, obtaining a photo of the carbon nanotube structure, the photo shows the at least one carbon nanotube and a background.