The invention belongs to the field of auxiliary electric power equipment, and particularly relates to an external wallboard with waterproof structures for transformer substations. The external wallboard comprises an upper prefabricated board and a lower prefabricated board. The upper prefabricated board and the lower prefabricated board are mutually fitting arranged in the up-down direction, a protrusion which is used for being inserted into the lower prefabricated board is arranged at the bottom of the upper prefabricated board, a groove which is used for being matched with the protrusion is formed in the lower prefabricated board, the protrusion is arranged in a trapezoidal manner, a drain pipe is arranged at the bottom of the groove and is obliquely downwardly arranged from the inside to the outside, the upper prefabricated board and the lower prefabricated board comprise base layers and reinforcement layers, the base layers are arranged in the middles of the upper prefabricated board and the lower prefabricated board, the corresponding reinforcement layers are arranged on two sides of each base layer, a waterproof mortar layer is arranged on the side, which is far away from the corresponding base layer, of each reinforcement layer, and antistatic coating layers are further arranged on the outer surface of the upper prefabricated board and the outer surface of the lower prefabricated board. The external wallboard has the advantages that the upper prefabricated board and the lower prefabricated board are mutually fittingly arranged, accordingly, waterproof purposes can be effectively achieved by the aid of layering structures and mutually matched structures of the upper prefabricated board and the lower prefabricated board, and heat-insulation, sound-insulation, fireproof, anti-seismic and antistatic purposes can be achieved.