A　narrow　backfill　zone　is　formed　when　retaining　walls　are　built　near　existing　stabilized　structures　(e.g.,　rock　faces).　In　such　circumstances,　the　classical　passive　earth　pressure　coefficient　is　no　longer　applicable,　and　a　correction　factor　is　required　for　the　design.　This　paper　aims　to　develop　analytical　solutions　for　estimating　the　passive　earth　pressure　problem　of　narrow　cohesive-frictional　backfills　behind　retaining　walls.　The　novel　arched　differential　element　method　considers　both　effects　of　the　horizontal　shear　stress　in　backfills　and　the　soil　arching,　and　it　is　employed　to　estimate　the　passive　earth　pressure　distribution　along　with　wall　depth.　The　solutions　are　compared　against　those　published　experimental　data,　analytical　approaches,　and　finite-element　limit　analysis　solutions.　The　factors　influencing　the　distribution　of　passive　earth　pressure　are　also　undertaken　using　a　series　of　parametric　studies.　To　implement　the　derived　solutions　into　a　routine　design,　a　modified　practical　design　equation　is　presented　following　the　standard　Coulomb＇s　solutions.　This　work　provides　a　theoretical　guideline　for　the　initial　design　of　retaining　walls　with　narrow　soils,　and　it　should　be　of　great　interest　to　practitioners.