Abstract: Under the action of external complex alternating loads, the weld was easy to occur fatigue crack, which would cause damage to the structure. The tunnel magnetoresistance sensor was used to collect the self-magnetic flux leakage field signals in the weld fatigue damage process, and the waveform and amplitude variation characteristics of the detection signals with different fatigue loading cycles were obtained. The correctness of testing results was verified by the finite element simulation software. The results showed that, in crack initiation stage, the waveform distribution of detection signals changed significantly before and after loading. When the number of fatigue loading cycles continued to increase, the waveform and amplitude of signals fluctuated in a small range. After crack initiation, the detection signals were affected by the magnetic flux leakage field of the crack, and the amplitudes of signals increased inversely. In the early stage of crack propagation, the amplitudes increased slowly due to the limitation of crack length and tip opening angle. In the middle and later stage of crack propagation, the crack length and tip opening angle increased rapidly, and the amplitudes of signals also increased rapidly. After the fracture, the magnetic field signals were obviously reversed, and the fracture could be judged by the change of magnetic field polarity. Through the detection and analysis of self-magnetic flux leakage field in the weld fatigue damage process, the research results provided support to determine the fatigue damage state.