With continuous improvement of transmission voltage classes of the electrical power system and the transmission capacity,the traditional electromagnetic current transformer has exposed many problems and has been difficult to meet the needs of current society.The basic theory of optical fiber current transformer was studied,and the mathematical model of the optical fiber current transformer was established on this basis.According to the model,the optical fiber current transformer system was designed,and the related devices were chosen based on the optical path.And according to the characteristics of the output signal light path system,driver circuit of the laser and signal detection circuit of optical fiber current transformer were designed to test the performance of the detection circuit separately.Finally,accuracy testing system of the optical fiber current transformer was designed,and the optical fiber current transformer system was tested.Test results show that under the same test environment,the output of the optical fiber current transformer has a very good linear property,and the test results agree with IEC 0.2S-class.