The　adaptive　finite　element　limit　analysis　(AFELA)　method　was　employed　to　simulate　the　active　failure　mechanisms　and　plastic　region　distribution　properties　under　complex　backfill　conditions　to　study　the　active　earth　pressure　of　backfill　near　a　firm　slope　on　gravity　walls　rotating　about　the　bottom.　The　simulation　results　revealed　that　the　backfill　progressively　fails　from　top　to　bottom　and　the　backfill　in　the　area　above　the　failure　surface　enters　a　plastic　state.　The　slip　-line　method　was　combined　with　the　pseudo　-static　technique　to　compute　the　seismic　active　earth　pressure.　Compared　with　the　traditional　limit　analysis　method　and　limit　equilibrium　method,　the　seismic　slip　line　method　does　not　need　to　pre　-assume　the　failure　mechanisms.　The　reliability　and　rationality　of　the　method　are　confirmed　by　comparing　the　computation　results　of　the　seismic　slip　line　method　with　the　computation　results　of　the　finite　element　limit　analysis　method,　the　existing　experimental　data,　and　the　existing　theoretical　solutions.　Furthermore,　the　impacts　of　parameters　such　as　backfill　geometries,　seismic　acceleration,　and　interface　strength　on　seismic　active　earth　pressure　are　discussed　in　detail.