The invention discloses an ultra small-electric size electromagnetic resonant unit, a left-handed medium formed by the same and an application. The resonance unit includes a substrate and two parallel 1/2 wavelength open-circuited transmission lines arranged on the substrate; the two parallel transmission lines are spirally arranged in a coiled manner; the two parallel transmission lines can be excited by an electric field and a magnetic field simultaneously under electromagnetic waves so as to generate electric resonance and magnetic resonance; a plurality of resonant units can be connected together along the same line through coupled inductors so as to be arranged to form a resonant group; a plurality of resonant groups are arrayed at intervals in parallel at the same plane so as to form a resonant layer; and a plurality of resonant layers are stacked along a vertical direction so as to form the left-handed medium. The resonant unit of the invention can form a superbly uniform artificial medium, and the defect of low uniformity of a traditional continuous medium such as Teflon can be eliminated, and therefore, the artificial medium can be applied in practice, and the original characteristics of the artificial medium can be maintained. The resonant unit can be widely applied to the field of various kinds of artificial media.