In　the　area　of　high　seismic　intensity,　there　were　few　methods　for　calculating　active　earth　pressure　(E-a).　Especially　for　the　cantilever　retaining　wall　with　long　relief　shelf　(CRW-LRS),　the　theoretical　method　lags　behind　the　practical　engineering.　The　seismic　active　earth　pressure　(E-S)　of　the　CRW-LRS　subject　to　translational　mode　was　researched.　By　finite　element　method　(FEM),　the　failure　mode　of　the　active　limit　state　under　seismic　load　was　evaluated.　The　results　show　that　the　backfill　behind　the　wall　generates　the　first　sliding　surface　at　the　wall　heel　bottom,　the　second　at　the　wall　heel　top,　and　the　third　at　the　relief　shelf　top.　The　calculation　formula　of　E-S　under　long　relief　shelf　failure　mode　was　proposed　using　the　limit　analysis　method　of　a　horizontal　differential　layer.　The　calculation　results　were　compared　with　the　FEM　results　to　prove　the　rationality　and　reliability　of　the　theoretical　solution.　The　effects　of　relief　shelf　relative　length　(l)　and　position　(m),　wall　heel　length　(n),　internal　frictional　angle　of　the　backfill　(phi),　seismic　horizontal　acceleration　(a(h)),　and　seismic　vertical　acceleration　(a(V))　on　E-S　were　studied.