The invention discloses a system for testing the frequency response characteristic of an optical fiber current transformer. The system for testing the frequency response characteristic of the optical fiber current transformer comprises a data recording and analyzing device and a voltage generator used for generating modulating voltage signals, wherein the output end of the voltage generator is externally connected with the photoelectric modulation input end of the optical fiber current transformer, the input end of the data recording and analyzing device is externally connected with the output end of the optical fiber current transformer and is also connected with the output end of the voltage generator, the data recording and analyzing device is used for recording modulating voltage data output by the voltage generator and data output by the optical fiber current transformer and analyzing the data, and then the frequency response characteristic of the optical fiber current transformer is calculated. The invention further discloses a testing method of the system. According to the system and method for testing the frequency response characteristic of the optical fiber current transformer, closed-loop signals of the optical fiber current transformer are processed firstly, the analog modulation phase is introduced when the signals are processed, the optical nonreciprocity Farady phase caused by currents of a power line under different frequencies is simulated, and then the frequency response characteristic of the optical fiber current transformer is tested.