The　interesting　to　assess　the　condition　of　a　structure　with　structural　health　monitoring　data　has　gained　many　attentions.　Most　of　the　existing　methods　require　the　measurement　at　the　force　location.　This　paper　presents　a　novel　output-only　condition　assessment　method　that　does　not　require　measurement　at　the　force　location.　The　unknown　structural　damage　indices　and　input　force　can　be　identified　with　the　stochastic　gradient　descent　method.　The　dynamic　acceleration　response　sensitivities　with　respect　to　the　unknown　structural　damage　indices　and　input　force　are　derived　analytically.　Both　unknown　damage　indices　and　unknown　input　force　can　be　identified　by　minimizing　the　discrepancy　between　the　measured　and　calculated　vibration　data.　Numerical　studies　on　a　two-dimensional　truss　and　seven-floor　frame　and　experimental　studies　on　a　steel　frame　structure　are　presented　to　verify　the　accuracy　and　efficiency　of　the　proposed　method.　Results　demonstrate　that　the　damage　severity,　location,　and　unknown　input　force　can　be　identified.　Also,　the　measurement　at　the　force　location　is　not　required.　Furthermore,　when　20%　measurement　noise　is　considered,　the　identified　error　is　less　than　5%.