The invention discloses a method for preparing a carbon nanotube with specific quantities of walls and specific diameters. The method comprises the following steps of: (1) loading markers on a carbon nanotube which is placed in a multi-wall carbon nanotube horizontal array( on a substrate on which a groove is formed), strides over the groove and grows in a suspended mode; (2) fixing two ends of the carbon nanotube which grows in a suspended mode on a probe; moving the probe, pulling cut the outer wall of the carbon nanotube which grows in a suspended mode when a distance between two markers is monitored to be enlarged; continuously moving the probe to prepare the carbon nanometer which has removed outer wall; and monitoring the pull-cut process by a microscope; and (3) repeatedly performing the step (2) and the step (3) to prepare the carbon nanotube with specific quantities of walls and specific diameters. Compared with the conventional preparation method, the method can be carried out under an optical microscope, is easy to operate and is high in controllability; and the inner layer of the multi-wall carbon nanotube with the length of more than centimeter grades can be continuously drawn out so as to have the significance in preparing the carbon nanotube with specific quantities of walls and specific diameters.