This　paper　presents　the　analytical　experimental　modal　analysis　on　the　Qinzhou　Cable-Stayed　Bridge　in　Fuzhou,　China　with　a　main　span　of　605　m,　which　is　the　longest　among　the　completed　composite-deck　cable-stayed　bridges　all　over　the　world.　The　field　ambient　vibration　tests　on　the　bridge　deck　were　conducted　just　prior　to　opening　of　the　bridge..　The　output-only　data　modal　parameter　identification　was　carried　out　by　using　the　peak　picking　of　average　normalized　power　spectral　densities　(ANPSDs)　in　frequency-domain　and　stochastic　subspace　identification　in　time-domain.　It　is　demonstrated　that　the　ambient　vibration　tests　are　sufficient　to　identify　the　most　significant　modes　below　1.0　Hz　of　large　span　cable-stayed　bridges.　These　identified　modal　parameters　will　serve　as　a　basis　in　the　finite　element　model　updating,　structural　damage　detection,　condition　assessment,　and　long-term　health　monitoring　on　service.