Compared with the traditional magneto-resistive sensors, the giant magneto-resistance sensor has the advantages of high sensitivity, good reliability, wide measuring range, poor environment adaptability, small volume etc. The new measurement method of large current in power system is always a hot problem. For the current signal in power system is composed of fundamental frequency and higher harmonics, it is necessary to use a kind of magnetic sensor which has a wide frequency range. And the giant magneto-resistance (GMR) sensor has the advantages of wide measuring range meets the requirements. However, there is still a difficult problem to assess the dynamic characteristics of GMR with higher harmonics. This paper presents a new test method: The Helmholtz coil is used as the magnetic field generating device. The data acquisition card is used as the signal receiving and transmitting device. We program the computer to realize the automatic acquisition and processing of the sensor’s output signal. This paper firstly does the static characteristic test of the GMR sensor. On the basis of the results, the different frequency magnetic field is tested using the above method. This paper realizes the measurement of the dynamic characteristics of the giant magneto-resistance sensor to a certain extent .It provides a new train of thought for the analysis of the dynamic characteristics of giant magneto-resistive sensor.