The invention discloses a mutual inductor transient testing device with a controllable amplifiable Rogowski coil differential signal and a testing method thereof. The mutual inductor transient testing device comprises an upper computer. The upper computer is connected with a testing host computer. The main CPU module of the testing host computer is connected with a DA module. The DA module is connected with a power amplifier. The power amplifier is connected with the input end of the Rogowski coil of a tested electronic mutual inductor. The output end of the Rogowski coil of the tested electronic mutual inductor is connected with a controllable-gain voltage amplifier. The controllable-gain voltage amplifier is connected with an acquisition unit of the tested electronic mutual inductor. The acquisition unit of the tested electronic mutual inductor is connected with a merging unit. The merging unit is connected with a data receiving module of the testing host computer. The mutual inductor transient testing device settles technical problems such as high condition requirement and high investment in transient simulation testing hardware test on a Rogowski coil principle electronic current transformer, great current amplitude increase in testing, and a large number of attenuation DC components and harmonic wave components contained in a fundamental wave component in an intelligent transformer substation and a digital transformer substation.