At　present,　long　span　cable-stayed　bridge　seismic　performance　study　only　takes　its　main　bridge　as　an　analysis　object.　There　are　few　reports　about　earthquake　impact　between　a　cable-stayed　bridge　and　its　approach-bridge.　Taking　a　Jiu-Jiang　big　bridge　as　an　example,　the　impact　analysis　model　between　a　cable-bridge　and　its　approach-bridge　was　built.　The　impact　influence　factors　between　them　were　systematically　studied.　The　influence　factors　included　site-type,　height　of　gravity　center,　approach-bridge　structure　form.　Some　significant　conclusions　were　obtained.　They　provided　a　reference　for　similar　project　a　seismic　designing.