Abstract: The dynamic tensile tests of 16MnR steel under the weak magnetic field excitation have been conducted to investigate the damage detection problem. In order to solve the problem, a new array magnetic sensor was designed based on giant magneto resistive chip, and a magnetic signal detection system was built firstly. Then, the magnetic signal of specimen surface was picked up in different stages of loading, and the noise was suppressed effectively with the wavelet transform. Finally, the magnetic signal was scanned after noise reduction was processed to achieve the magnetic signal imaging display in the development process of damage. So a new reign detection method is provided for fatigue damage of the ferromagnetic specimen.