When　the　finite　element-strength　reduction　method　is　used　for　two-dimensional　slope　stability　analysis　for　elastic-perfectly　plastic　material,　the　failure　criterion　usually　adopts　the　criterion　of　plastic　zone　penetration.　That　is,　when　the　slope　is　in　the　limit　equilibrium　state,　the　plastic　zone　goes　through　the　slope　from　the　toe　to　the　top.　Meanwhile,　the　critical　slip　surface　is　composed　of　a　series　of　points　of　maximum　equivalent　plastic　strain　along　the　depth　direction.　By　deploying　a　set　of　parallel　lines　approximately　perpendicular　to　the　slope　surface　and　picking　out　the　points　of　these　lines　with　the　maximum　equivalent　strain　points,　we　obtain　a　series　of　points　taking　on　a　wave　shape,　which　constitutes　a　signal　function.　Subsequently,　the　wavelet　packet　analysis　is　used　to　smooth　these　points,　i.e.,　locating　the　critical　slip　surface.　The　analysis　of　classic　examples　and　comparison　with　Spencer＇s　method　show　that　the　proposed　method　in　this　paper　is　reasonable　and　effective.