Based　on　the　analysis　of　the　stratum＇s　location　and　composition　in　Fuzhou　city,　it　is　found　that　stratum　structure　is　important　and　can　be　divided　into　two　types.　In　order　to　get　a　further　acquaintanceship　about　the　pit＇s　working　behavior　in　soft　clay,　a　planar　strain　finite　element　programme　is　employed　for　numerical　analysis.　Mohr-Coulomb　model　is　used　to　simulate　the　soil＇s　stress　and　strain　relation.　A　series　of　calculations　via　FEM　are　executed　for　the　displacement　response　of　foundation　pits　when　the　type　of　stratum　structure,　length　or　obliquity　of　soil　nailing　are　changed.　Compared　with　the　pit＇s　parietal　movement　under　different　conditions,　some　significant　conclusions　are　obtained　that　the　prepositive　pile　is　the　most　important　affecting　factor　for　composite　soil　nailing.　The　cement　mixed　pile　should　be　chosen　for　the　prepositive　pile　of　double　stratum,　and　timber　pile　for　three　stratum.　Because　of　the　clay＇s　weaker　properties　and　wider　sliding　route　than　those　of　the　others,　the　length　of　the　soil　nailing　should　be　added　to　two　times　of　the　pit＇s　depth　which　is　different　from　that　of　those　located　in　favorable　soil.　Finally,　two　cases　are　optimized　based　on　above　analysis,　indicating　a　good　identicalness　between　the　results　of　calculation　and　measurement.