The　modification　of　the　planar　double-enveloping　hourglass　worm　gear　drive　can　eliminate　the　phenomenon　of　the　contact　line　cross　and　improve　the　transmission　performance.　In　order　to　guide　the　selection　of　the　type　and　the　amount　of　modification,　the　equations　of　the　contact　zone　and　rear　transition　zone　on　the　worm　wheel　surface　are　established.　According　to　the　position　relationship　between　the　contact　zone　and　the　rear　transition　zone　on　the　axial　plane　and　transverse　plane,　the　changes　in　the　tooth　surface　of　the　worm　wheel　obtained　by　different　modification　methods　are　obtained.　The　tooth　surface　changes　obtained　under　different　modification　amounts　are　further　summarized　The　structure　of　the　modified　worm　wheel　is　finally　determined.　For　Type-II　drive　processed　with　the　center　distance　modification,　the　curvature　interference　limit　line　on　the　surface　of　the　worm　wheel　can　be　cut　off　by　the　last　cutting　edge　of　the　hob.　The　larger　the　amount　of　the　center　distance　modification　value　is,　the　deeper　the　depth　into　the　rear　transition　zone　is.　Finally,　the　analysis　results　were　verified　by　the　hobbing　experiment　and　the　worm　gear　drive　running　test.