A carbon nanotube (CNT) assembled thin film modified steel wire array electrode, a preparation method and application thereof. The array electrode includes: a surface of a steel wire is negatively modified, and the surface of the steel wire is assembled with a plurality of layers of CNT thin films; one end of the steel wire is welded to a conductor, and a welding position between the steel wire and the conductor is wrapped with an insulating heat shrinkable tube; and the insulating template and the steel wire are encapsulated and cured by using an epoxy resin. The preparation method of the array electrode of the invention mainly includes the following steps: first, performing negative modification on a steel wire, then, assembling CNT thin films on the steel wire, and preparing the modified array steel wire into the CNT assembled thin film modified steel wire array electrode.