A high-impedance transformer simulation on-load current flowing test device and test method is provided. The test device includes an electronic three-phase broadband power supply, a three-phase large-current generator, and a broadband wireless phase telemetry device. The output end of the electronic three-phase broadband power supply is connected to the three-phase power-frequency large-current current riser. The three-phase power-frequency large current of the current riser are composed of three isolation transformers having the same specification and model. Before the measurement, time calibration is performed on a host and an extension of the broadband wireless telemetry phase device, the power-frequency current flowing and low-frequency current flowing are performed, the correctness ofa differential protection hexagonal diagram is detected, a transformation ratio is measured, the correctness of the transformation ratio the polarity is determined, and differential current calculation is performed. The test device ensures the safe and stable operation of the system and improves the one-time operation success rate.