The invention discloses a fractal-structure acoustic metamaterial device used for noise reduction of a transformer. A fractal-structure acoustic metamaterial (1) of the device is fixed by a metamaterial framework (3) and is placed into a metamaterial supporting support (4). The metamaterial supporting support (4) is placed in front of a ventilation opening of the transformer and is parallel to theventilation opening of the transformer. The fractal-structure acoustic metamaterial (1) is of a cuboid structure with an acoustic wave waveguide (2) and a bottom plate, and air circulates in the fractal-structure acoustic metamaterial (1) along the acoustic wave waveguide (2). When acoustic waves are transmitted to the fractal-structure acoustic metamaterial (1), the acoustic wave amplitude of atarget area is greatly reduced due to the characteristics of strong reflection and the equivalent high refraction rate.