A fiber optic differentiating current sensor based on magnetostriction effect is designed.The sensor can be used in high sensitivity,high accuracy measurement for electrical currents and magnetic field.The principle of the sensor is analyzed,and the theoretical model is developed and verified through experiments.Employing the proposed system,the input output performances,offset performances,and accuracy of the sensor were experimentally demonstrated,and a ratio error of about 0.5 % was achieved in measured current range from 8 A to 200 A.