For the measurement of AC current,an optical current transformer(OCT) based on distributed feedback(DFB) demodulation is proposed.The fiber Bragg grating(FBG) and the giant magnetostrictive material(GMM) are used as the sensor probe of the current transformer.By using the DFB laser,we realize the demodulation of fiber grating and the measurement of alternative current.By theoretical analysis and experiment,the sensing sensitivity of the system can reach 11.822×10-3 nm/A with 0.63% full scale accuracy,and the linearity-fitted degree is 0.996 2.So it is suitable for detection of small current with high-precision.