Abstract: To address the issue of fatigue damage detection of ferromagnetic key components in service, the fatigue damage of 45# steel specimens by magnetoacoustic emission (MAE) was carried out. A variety of typical characteristic parameters were extracted from the MAE time-domain waveforms, frequency spectra and magnetoacoustic hysteresis curves, and the relationships between the conventional and equivalent hysteresis characteristic parameters and fatigue damage were analyzed. Results show that different regularities with fatigue cycle are present in the four typical characteristic parameters extracted, and there are significant differences in the characterization ability and sensitivity range of them for the fatigue degree. With the increase of fatigue cycle, the half-period energy and equivalent residual flux density first increase and then decrease. Wherein half-period energy is more sensitive to the early fatigue state changes, and equivalent residual flux density is more sensitive to the state change in the late fatigue stage. In addition, the equivalent coercive force and gravity frequency show an approximate monotonic variation with fatigue loading, which is suitable for the characterization of fatigue process. The gravity frequency is more sensitive to the early fatigue state, and the monotonic variation of the equivalent coercivity with fatigue is more regular. The research provides a feasible technical solution for condition monitoring and quantitative characterization of ferromagnetic materials during fatigue loading.