Abstract: To ensure the safe and reliable operation of oil and gas pipelines, it is necessary to monitor the fatigue crack propagation process of pipeline structures in real time. Based on tensile-tensile fatigue tests on notched 45 steel specimens, multi-parameter micromagnetic nondestructive testing technology was used to comprehensively monitor the entire process of fatigue damage evolution in situ, and the collected magnetic signals were parametrically analyzed. Test results showed that as the number of load cycles increased, characteristic parameters such as magnetic hysteresis, magnetic Barkhausen noise, and incremental permeability exhibited trends of initial fluctuations, mid-term stability, and later sudden changes, which were basically consistent with the law of metal fatigue crack propagation. Among them, the incremental permeability parameter signal had the highest sensitivity to the initiation and propagation of fatigue cracks. Its Mean eigenvalue could quantitatively assess the degree of damage, and the Mean zero-value line could serve as an early warning for imminent fatigue failure of components. This provided a new approach for predicting the fatigue life of engineering materials or structures.