The　general　mathematical　model　of　internal　meshing　spiral　bevel　gears　for　nutation　drive　is　studied.　Based　on　conventional　enveloping　theory　and　transmission　principle,　the　meshing　of　two　spiral　bevel　gears　in　nutation　drive　was　substituted　by　the　meshing　of　an　imaginary　rotating　crown　gear　engaging　with　the　external　and　internal　bevel　gear　respectively.　The　general　mathematical　model　of　crown　gear　was　established.　Then　the　general　mathematical　model　of　internal　meshing　spiral　bevel　gears　is　obtained　by　matrix　transformation,　which　is　suitable　for　a　variety　of　gear　tooth　profiles.　Finally,　the　mathematical　model　and　3D　modeling　of　double　circular-arc　spiral　bevel　gears　are　developed.　©　(2012)　Trans　Tech　Publications.