The invention discloses an auxiliary current transformer, comprising a cabinet body; a transformer, an electric reactor, an inverter and an exhaust air assembly are installed in the cabinet body; the electric reactor and the inverter are respectively installed at relative sides of the transformer; the exhaust air assembly is installed at the side of the transformer adjacent to the electric reactor; a first air inlet channel is formed between the electric reactor and the cabinet body; a second air inlet channel is formed between the inverter and the cabinet body; an exhaust air channel is formed between the transformer and the cabinet body; an air guide assembly is arranged at the bottom of the cabinet body; the air inlet of the air guide assembly is connected with the first air inlet channel and the second air inlet channel; the air outlet is connected with the air inlet of the exhaust air assembly; the air outlet of the exhaust air assembly aligns to the air inlet of the exhaust air channel; the side in the transformer relative to the exhaust air assembly is equipped with an exhaust air cavity; the air inlet of the exhaust air cavity is connected with the air outlet of the exhaust air channel; and the air outlet of the exhaust air cavity is arranged downward. The auxiliary current transformer of the invention is advantaged by simple and compact structure and adjustable air inlet quantity and air speed.