The　embankment　of　an　S-shaped　gully　(E-SSG)　has　a　specific　topography,　which　results　in　its　unique　shape　effect.　However,　how　the　shape　effect　of　the　E-SSG　is　generated,　how　it　relates　to　different　geometric　variables,　and　how　it　can　be　considered　in　slope　stability　analysis　remain　unknown.　Hence,　this　study　examined　this　shape　effect　using　the　finite-element　strength　reduction　method　to　analyze　the　spatial　stress　and　displacement　distribution.　In　addition,　the　gray　correlation　method　was　introduced　to　determine　the　link　between　the　shape　effect　and　the　terrain　factors.　Furthermore,　the　shape　effect　within　the　steep　slope　of　an　E-SSG　was　considered　and　a　dimension-reduced　(DR)　slope　stability　analysis　technique　was　proposed.　Upon　obtaining　the　link　between　the　shape　effect　and　the　terrain　factors,　the　shape　effect　factor　ψ　can　be　calculated.　A　ψ　value　＞0.062　indicated　a　shape　effect　on　the　E-SSG.　On　this　basis,　the　three-dimensional　safety　coefficient　of　the　E-SSG　can　be　obtained　using　the　spatial-effect　trends　and　the　safety　factor　via　the　DR　approach　(i.e.,　the　two-dimensional　model).　Finally,　the　rationality　and　accuracy　of　the　proposed　method　were　validated　using　engineering　cases.　Moreover,　generation　mechanisms　and　principal　determinants　of　the　shape　effects　within　the　steep-slope　embankments　under　S-shaped　and　V-shaped　gullies　were　compared.　It　was　learned　that　the　E-SSG　is　an　asymmetric　structure　compared　with　the　V-shaped　gullies,　and　the　stable　right　base　bank　is　an　important　factor　in　the　shape　effect　of　the　E-SSG.　©　2025　American　Society　of　Civil　Engineers.