Beam　string　structure　(BSS)　is　introduced　as　a　new　type　of　hybrid　prestressed　string　structures.　The　composition　and　mechanics　features　of　BSS　are　discussed.　The　main　principles　of　wavelet　packet　transform　(WPT),　principal　component　analysis　(PCA)　and　support　vector　machine　(SVM)　have　been　reviewed.　WPT　is　applied　to　the　structural　response　signals,　and　feature　vectors　are　obtained　by　feature　extraction　and　PCA.　The　feature　vectors　are　used　for　training　and　classification　as　the　inputs　of　the　support　vector　machine.　The　method　is　used　to　a　single　one-way　arched　beam　string　structure　for　damage　detection.　The　cable　prestress　loss　and　web　members　damage　experiment　for　a　beam　string　structure　is　carried　through.　Different　prestressing　forces　are　applied　on　the　cable　to　simulate　cable　prestress　loss,　the　prestressing　forces　are　calculated　by　the　frequencies　which　are　solved　by　Fourier　transform　or　wavelet　transform　under　impulse　excitation.　Test　results　verify　this　method　is　accurate　and　convenient.　The　damage　cases　of　web　members　on　the　beam　are　tested　to　validate　the　efficiency　of　the　method　presented　in　this　study.　Wavelet　packet　decomposition　is　applied　to　the　structural　response　signals　under　ambient　vibration,　feature　vectors　are　obtained　by　feature　extraction　method.　The　feature　vectors　are　used　for　training　and　classification　as　the　inputs　of　the　support　vector　machine.　The　structural　damage　position　and　degree　can　be　identified　and　classified,　and　the　test　result　is　highly　accurate　especially　combined　with　principle　component　analysis.