The invention relates to a warming box for a transformer calibrator. The warming box comprises a box body and a box cover. The box body comprises an inner layer and an outer layer. A glass fiber insulation layer is arranged between the inner layer and the outer layer. A platform is arranged in an inner chamber of the box body. Supporting columns are arranged below the box body. The supporting columns, the platform and the inner wall of the box body form an airflow duct. An electric fan heater is arranged under an inner wall platform of the box body. An electronic temperature control switch is arranged on the inner wall of the box body. Heat flows generated in the box body increase outer temperature of the transformer calibrator, thus sufficient heat is guaranteed and used to support the transformer calibrate to operate in a low temperature environment.