The invention provides a nanodiode preparation method and a nanodiode. The method comprises the steps: preparing a carbon nanotube; depositing at least one semiconductor crystal on the carbon nanotube, wherein each semiconductor crystal and the carbon nanotube wrapped by the semiconductor crystal form a semiconductor heterojunction; locating a drain electrode region on the semiconductor heterojunction and a source region on a carbon nanotube segment connected with the semiconductor heterojunction; controlling the deposition of the drain electrode of a diode in the drain electrode region and the deposition of the source electrode of the diode in the source electrode region, wherein the drain electrode, the source electrode, the semiconductor heterojunction for depositing the drain electrode and the carbon nanotube segment for depositing the source electrode form the nanodiode. According to the scheme provided by the invention, the method breaks through the physical limits of the Moore's law.