The invention relates to a single-layer gold nano-structure capable of realizing asymmetric transmission and a preparation method thereof. The single-layer gold nano-structure is prepared through the following ten steps of: preparing a substrate; applying photoresist; performing post-photoresist application drying; using an electron beam to expose the pattern of the structure; performing developing; performing fixation; performing post-fixation drying; performing gold plating; stripping the photoresist; and performing drying. The single-layer gold nano-structure of the invention is of structural simplicity; the single-layer gold nano-structure has connectivity, so that the coupling of light and the metal micro-nano structure can be enhanced, and the asymmetric transmission characteristic of the light can be realized; and the length of first vertical bodies of the single-layer gold nano-structure and the length of third bodies of the single-layer gold nano-structure are set to be unequal, and therefore, the single-layer gold nano-structure has two more resonance modes than a structure with first vertical bodies and third vertical bodies which are equal in length, and thus, the adjustment of a plurality of frequency bands can be realized, and two relatively large asymmetric transmission effects can be generated. According to the preparation method of the invention, in the exposure process of the pattern of the structure, the electron beam etches a part of the pattern of the structure, and therefore, the exposure time of the pattern of the structure is saved, and preparation efficiency can be improved.