Based　on　wheel-rail　contact　relationship　and　dynamic　interaction　when　wheel　treads　pass　from　wing　rail　to　nose　rail,　a　design　and　evaluation　method　for　nose　depth　selection　of　key　cross-sections　was　proposed　to　select　reasonable　nose　depths　for　rigid　frog.　A　train　with　LMA　wheel　treads　passing　over　No.　12　turnout　of　rigid　frog　in　the　facing　move　of　the　straight　direction　was　taken　as　an　example,　and　the　optimization　of　nose　depths　was　carried　out　by　this　method.　The　research　results　show　that　the　nose　depths　of　key　cross-sections　should　not　only　satisfy　the　safety　of　wheel-load　transition　and　the　strength　of　nose　rail,　but　also　improve　the　train　running　stability.　The　smaller　the　nose　depth,　the　smaller　the　wheel-rail　interaction,　which　is　helpful　to　improve　the　running　performance,　but　whether　the　wheel-rail　interaction　location　exceeds　the　scope　of　nose　bearing　capability　should　be　taken　into　account.　To　a　No.　12　turnout　of　rigid　frog,　the　optimal　nose　depths　of　the　cross-sections　with　railhead　widths　of　20　and　50　mm　should　be　3　and　0　mm　respectively.　©　2015,　Editorial　Department　of　Journal　of　Southwest　Jiaotong　University.　All　right　reserved.