The invention discloses an optical fiber current transformer device and a current measuring method thereof. The device comprises an integrated light transceiving phase modulator, a circuit module, anoptical fiber delay ring and an optical fiber sensing ring, and the integrated light transceiving phase modulator generates optical wave signals and converts the signals into two beams of linearly polarized light which are orthogonal to each other; the circuit module is used for providing a driving circuit for the integrated light transceiving phase modulator and calculating a current measuring result according to a phase difference result output by the integrated light transceiving phase modulator; the optical fiber delay ring is used for transmitting the optical wave signals; the optical fiber sensing ring is used for transmitting the phase difference generated according to the Faraday magnetic-optical effect back to the integrated light transceiving phase modulator; the integrated lighttransceiving phase modulator comprises a power source chip, a Y waveguide chip, a straight waveguide chip and a probing chip. By means of the optical fiber current transformer device and the currentmeasuring method thereof, the light path melting difficulty of an optical fiber current transformer is lowered, and engineering development of the optical fiber current transformer is facilitated.