Among　the　common　early　mechanical　property　degradation　damage　of　metal　materials,　fatigue　has　the　greatest　potential　harm　to　the　structure.　Based　on　the　hysteresis　nonlinearity　of　ferromagnetic　materials,　the　mechanism　and　manifestation　of　magnetic　frequency　mixing　effect　in　ferromagnetic　materials　under　high　and　low　frequency　excitation　are　analyzed.　The　relationship　between　the　mixing　component,　the　local　hysteresis　loops　and　the　early　damage　of　magnetic　ferromagnetic　materials　is　analyzed.　The　magnetic　mixing　nonlinear　factor　and　the　power　law　coefficient　of　local　hysteresis　loss　are　proposed　to　characterize　the　magnetic　frequency　mixing　effect　of　ferromagnetic　materials.　Then,　magnetic　frequency　mixing　detection　technology　is　used　to　detect　fatigue　damage　of　ferromagnetic　materials.　Experimental　results　show　that　the　early　fatigue　damage　of　ferromagnetic　materials　can　be　characterized　by　two　kinds　of　magnetic　mixing　characteristic　parameters.　This　research　work　provides　a　feasible　technical　scheme　for　early　fatigue　damage　detection　of　ferromagnetic　materials.　©　2020　Journal　of　Mechanical　Engineering.