Based　on　the　hypothesis　each　magnetic　domain　is　considered　as　a　MBN　emission　“source”;　a　layered　model　describing　the　generation　mechanism　and　propagation　attenuation　of　the　“source”　signal　is　built.　The　mathematical　description　of　the　MBN　derived　from　the　excited　ferromagnetic　materials　is　given.　According　to　this,　a　novel　multi-gradient　nondestructive　characterization　and　testing　method　is　proposed;　and　a　concept　“MBN　Multi-Gradient　NDT　&　E”　is　introduced　innovatively.　The　proposed　model　lays　the　theoretical　basis　for　“MBN　Multi-Gradient　NDT　&　E”;　and　links　the　division　of　MBN　frequency　bands　with　different　testing　gradients.　Then,　using　a　specimen　made　of　Q235　steel,　the　classic　four-point　bending　experiment　was　implemented.　The　MBN　eigenvalues　of　time　domain　voltage,　of　spectrum　density,　and　of　power　spectral　density　were　extracted　under　different　loadings.　The　final　results　showed　a　turning　point　under　some　specific　testing　gradients;　this　indicates　the　material　has　initial　yielded.　Comprehensive　analysis　of　all　results,　which　perfectly　reveal　the　inhomogeneous　layering　stress/strain　levels,　elastic/plastic　deformation　of　the　specimen　distributed　along　the　depth　direction.　The　proposed　“MBN　Multi-Gradient　NDT　&　E”　method　can　more　completely　and　fully　characterize　the　mechanical　properties　of　the　specimen　quantitatively　or　semi　quantitatively;　and　has　important　theoretical　and　practical　significance.　IEEE