The　deflection　which　reflects　the　bridge　linear　variety　is　an　important　parameter　for　the　evaluation　of　bridge　safety.　According　to　the　structural　characteristics　of　urban　bridges,　the　connected　pipe　optoelectronic　liquid　level　sensor　system　is　a　novel　kind　of　sensor　for　detecting　the　connected　pipe　liquid　level,　which　can　be　applied　for　multipoint,　long-period,　online,　remote,　automatic　measurement　of　bridge　deflection,　it　is　not　affected　by　the　dust,　humidity　and　fog　in　the　urban　bridge　health　monitoring　and　maintenance.　At　present,　the　system　has　been　integrated　and　applied　in　the　project　of　main　roads　bridge　Online　Safety　Monitoring　Management　System　in　Hangzhou　(Phase　II),　a　web-based　urban　bridge　cluster　monitoring　system　have　been　established　since　2007.　According　to　a　tied　arch　bridge　case　studies,　the　measuring　data　show　that　the　system　not　only　can　accurately　collect　the　bridge　normal　deflection　information　and　variety,　but　also　successfully　monitored　the　structural　responses　due　to　the　Wenchuan　earthquake　on　May　12,　2008.　About　two-minute　abrupt　changes　in　displacement　amplitude　were　observed　in　the　measured　signals　starting　at　14:37,　about　9　minutes　later　than　the　earthquake＇s　occurring.　The　results　shows,　it　is　an　effective　method　for　the　real-time　monitoring　of　urban　bridge　deflection.　©　(2012)　Trans　Tech　Publications,　Switzerland.