Abstract: The present invention discloses single-walled carbon nanotubes horizontal arrays with ultra-high density and the preparation method. The method comprises the following steps: loading a catalyst on a single crystal growth substrate; after annealing, introducing hydrogen into a chemical vapor deposition system to conduct a reduction reaction of the catalyst; and maintaining the introduction of the hydrogen to conduct the orientated growth of a single-walled carbon nanotube. The density of the ultra-high density single-walled carbon nanotube horizontal array obtained by this method exceeds 130 tubes/micrometer, and an electrical performance test is performed on the prepared ultra-high density single-walled carbon nanotube horizontal array shows a high on-current density of 380 ?A/?m, and the transconductance of 102.5 ?S/?m.