The invention relates to a transformer testing tool. The transformer testing tool includes a frequency conversion power supply, an adjustable load resistor, a PLC, a touch screen display control system and a test cabinet, wherein the PLC and the touch screen display control system are arranged at the upper end of the test cabinet; a mounting base and an alternating current contactor are arranged in the middle cabinet body of the test cabinet; the mounting base is used for holding the tested transformer; the alternating current contactor is connected with the frequency conversion power supply and the PLC; the alternating current contactor is also used for connecting the transformer to be tested; the PLC controls the frequency conversion power supply for providing voltage fluctuation and voltage impact for the tested transformer; the touch screen display control system connects the PLC and displays the set parameter information of the PLC and the state information of the test; the adjustable load resistor is arranged in the lower cabinet body of the test cabinet; and the adjustable load resistor is used for connecting the output terminal of the tested transformer. The transformer testing tool can realize practical application test reliability assessment for voltage fluctuation impact and overload operation of the transformer.