Magnetic　flux　leakage　(MFL)　method　is　a　non-destructive　method　commonly　used　for　equipment　with　ferromagnetic　material.　This　paper　presents　a　low　frequency　alternating　current　(AC)　excitation　MFL　method.　This　method　uses　low　frequency　AC　current　excitation　to　obtain　a　high　detection　depth,　and　to　realize　the　examination　of　internal　and　external　surface　of　the　ferromagnetic　structures.　Based　on　the　low　frequency　AC　excitation　simulation　model　built　in　ANSYS　Electronics18.1　software,　the　amplitude　and　phase　parameters　of　magnetic　field　were　extracted　and　calculated.　With　the　changes　of　the　defect　depths　in　different　positions　of　the　steel　plate,　the　results　of　amplitude　and　phase　parameters　of　magnetic　field　were　studied　and　analyzed.　Then　the　experiments　of　detection　on　artificial　defects　with　different　depths　in　different　positions　were　conducted.　The　simulation　and　experimental　results　were　discussed.　Copyright　©　2018　ASME.