Most　of　the　existing　output-only　damage　detection　methods　require　the　number　of　sensors　should　be　larger　than　the　number　of　unknown　excitation　force,　and　the　force　location　should　be　available.　This　paper　presents　a　novel　output-only　damage　detection　method　without　these　requirements.　The　proposed　method　is　based　on　the　correlation　function　of　acceleration　responses.　When　the　structure　is　under　white　noise　excitations　(or　ambient　excitations),　the　correlation　function　of　acceleration　responses　can　be　treated　as　free　vibration　responses　with　unknown　initial　conditions.　The　unknown　structural　parameters　and　initial　conditions　can　be　simultaneously　identified　by　minimizing　the　difference　between　the　measured　and　calculated　correlation　functions.　The　unknown　initial　conditions　are　identified　with　state　space　method　and　the　unknown　structural　parameters　are　updated　with　sensitivity　method.　Numerical　studies　of　a　2D　truss　and　a　five-bay　3D　frame　structure　are　conducted　to　demonstrate　the　accuracy,　effectiveness,　and　robustness　of　the　proposed　method.　Experimental　studies　on　an　eight-floor　steel　frame　are　further　carried　out.　Results　show　that　the　proposed　method　is　not　only　insensitive　to　environmental　noise　but　also　applicable　when　the　number　of　sensors　is　less　than　that　of　unknown　excitations.　Also,　the　proposed　method　can　be　used　for　damage　detection　when　the　force　location　is　unknown.