With the wide application of DC transmission line in the power system， the requirement on the accurate measurement of DC current is urgent. A novel DC current measurement method based on the giant magneto-resistance is presented. The static input-output characteristic of giant magneto-resistance sensor， and the influence of temperature are studied. On that basis， the overall structure of DC electronic current transformer is designed. The non-linear characteristic of the giant magneto-resistance sensor is analysed， and a non-linear compensation method proposed. Measurement results verify the proposed method.