This　study　utilises　adaptive　finite　element　analysis　to　investigate　the　failure　mechanisms　of　narrow　cohesive　backfill　under　seismic　conditions,　and　five　classical　failure　modes　are　summarized.　The　pseudo-static　solution　is　developed　for　the　case　when　a　narrow　cohesive　backfill　is　behind　a　gravity　retaining　wall　and　experiences　seismic　conditions.　Our　analytical　solution　uses　the　limit　equilibrium　method,　Rankine＇s　theory　and　the　horizontal　differential　layer　method.　It　considers　the　effect　of　soil　cohesion,　the　interface　friction　angles,　backfill　geometries,　seismic　acceleration,　the　soil　arching　effect　and　the　effect　of　shearing　forces　between　adjacent　elements　on　seismic　active　earth　pressure.　We　propose　a　new　approach　that　utilises　the　finite　difference　method　to　determine　the　tension　crack　depth　of　the　narrow　cohesive　backfill,　and　an　iterative　calculation　to　determine　the　critical　failure　angle　of　the　backfill　wedge.