Efficiency　is　one　of　the　most　important　characteristics　of　a　gear　transmission　system.　This　paper　focuses　on　the　efficiency　modeling　and　analysis　for　the　nutation　drive　with　double　circular　arc　spiral　bevel　gears.　The　transmission　efficiency　formula　of　the　nutation　drive　system　is　deduced　according　to　the　planetary　gear　drive　with　small　tooth　number　difference.　Then,　a　meshing　efficiency　model　of　the　double　circular　arc　spiral　bevel　gear　is　established　for　the　nutation　drive　system.　Further,　dynamic　and　relative　sliding　velocity　analyses　are　carried　out　for　the　double　circular　arc　spiral　bevel　gear　pair.　The　meshing　efficiency　formula　of　double　circular　arc　spiral　bevel　gear　is　set　up　by　considering　the　tooth　profile　normal　force,　relative　sliding　velocity　and　sliding　friction　coefficient.　Finally,　the　efficiency　analysis　influenced　by　the　nutation　angle,　gear　spiral　angle,　cone　distance　and　friction　coefficient　between　the　meshing　gear　pairs　are　discussed.　©　2017　Taylor　&　Francis　Group,　London.