At　the　beginning　of　the　21st　century,　Su-tong　and　Stonecutters　cable-stayed　bridges　were　born　into　the　world,　which　make　the　original　span　record　of　890m　up　to　1088m.　The　increasing　range　of　the　span　is　so　large　that　it　is　necessary　to　carry　out　a　special　research　on　structural　system　of　the　cable-stayed　bridge　with　kilometer-scale　span.　Therefore,　two　cable-stayed　bridges　have　been　designed　as　the　research　objects,　which　come　from　the　background　of　Su-tong　cable-stayed　bridge.　And　the　main　span　is　respectively　1308m　and　1500m.　In　this　paper,　an　analysis　is　carried　out　from　the　aspect　of　girder-tower　relationship　which　comes　from　the　concept　of　the　structural　system.　In　the　static　analysis,　structural　system,　which　is　respectively　floating,　half　floating　and　rigid,　has　been　studied.　And　in　the　dynamic　analysis,　the　girder-tower　relationship　has　also　been　studied,　which　is　respectively　with　no　dampers,　elastic　links　and　viscous　dampers.　Based　on　the　analysis　results,　structural　system　applicable　for　kilometer-scale　cable-stayed　bridges　is　summarized.