The utility model relates to an optical fiber current transformer, including full optical fiber sensing coil 1, polarization maintaining fiber 2 and collector 3, collector 3 includes that light source4, fiber coupler 5, the optic fibre polarizer 6, straight waveguide phase modulator 7, polarization maintaining fiber postpone ring 8, photoelectric detector 12, signal conditioning circuit 13, AD converter 14, processing module 15 and DA converter 16, and full optical fiber sensing coil 1 includes optic fibre wave plate 9, protects circle sensing fiber 10 and polarization maintaining fiber 011.Sensitization way phase place state can be exchanged through the closed loop feedback ring of photoelectric detector 12, signal conditioning circuit 13, AD converter 14, processing module 15 and 16 formation of DA converter and feedback control is carried out. Consequently, through the cooperation use and the closed loop feedback control of inside each components and parts of this current transformer, can promote optical fiber current transformer's detecting reliability, realize that the high reliability detects.