A　finite　element　model　was　built　for　MnBi/alpha-Fe　nanocomposite　permanent　magnets,　and　the　demagnetization　curves　of　the　magnets　were　simulated　by　micro-magnetic　calculation.　The　microstructure　of　the　cubic　model　is　composed　of　64　irregular　grains　with　an　average　grain　size　of　20　nm.　With　the　volume　fraction　of　soft　magnetic　phase　(t　vol.　%)　ranged　from　5　to　20　vol.　%,　both　isotropic　and　anisotropic　nanocomposite　magnets　show　typical　single-phase　permanent　magnets　behavior　in　their　demagnetization　curves,　illustrating　good　intergranular　exchange　coupling　effect　between　soft　and　hard　magnetic　phases.　With　the　increase　of　volume　fraction　of　soft　magnetic　phase　in　both　isotropic　and　anisotropic　magnets,　the　coercive　force　of　the　magnets　decreases　monotonically,　while　the　remanence　rises　at　first　to　a　peak　value,　then　decreases.　The　optimal　values　of　maximum　energy　products　of　isotropic　and　anisotropic　magnets　are　84　and　200　kJ/m(3),　respectively.　Our　simulation　shows　that　the　MnBi/alpha-Fe　nanocomposite　permanent　magnets　own　excellent　magnetic　properties　and　therefore　good　potential　for　practical　applications.