In　engineering,　retaining　walls　commonly　rotate　about　the　base　(RB)　and　narrow　backfill　is　often　compressed.　Current　methods　cannot　accurately　predict　the　passive　earth　pressure　of　a　narrow,　cohesionless　backfill　against　the　retaining　wall.　Therefore,　this　study　will　investigate　the　passive　failure　mechanism　of　narrow,　cohesionless　backfill　under　the　RB　mode　using　lower-bound　finite　element　limit　analysis　(FELA).　The　backfill　area　above　the　slip　surface　reached　a　plastic　state.　This　type　of　phenomenon　means　that　stress　deflection　occurs　in　a　narrow　backfill,　which　is　affected　by　the　boundary　conditions　on　each　side.　The　principal　stress　trajectory　is　assumed　to　be　a　concave　circular　arc.　In　addition,　a　method　to　determine　the　stress　trajectory,　stress　deflection　angle,　and　lateral　earth　pressure　coefficient　will　be　proposed　through　stress　analysis　of　soil　elements.　Moreover,　a　theoretical　method　to　calculate　the　passive　earth　pressure　in　a　narrow,　cohesionless　backfill　under　RB　mode　will　be　proposed　that　uses　the　limit　equilibrium　(LE)　method,　which　is　more　suitable　than　the　current　methods.　The　parameter　analysis　results　showed　that　decreasing　the　retaining　wall　slope　or　the　interface　friction　helps　to　reduce　the　earth　pressure　against　the　retaining　wall.　In　addition,　the　earth　pressure　at　the　bottom　of　the　wall　increases　significantly.　©　2020　American　Society　of　Civil　Engineers.