Free-interface　modal　synthesis　method　is　applied　to　civil　structure,　and　a　substructure　method　is　proposed　by　introducing　the　method　into　global　sensitivity　method.　The　substructure　expression　of　the　derivatives　of　eigenvalues　and　eigenvectors　with　respect　to　elemental　parameters　is　obtained.　The　accuracy　of　the　application　of　free-interface　modal　synthesis　method　is　evaluated　with　different　retained　modes　in　substructure,　and　then　the　effectiveness　of　the　proposed　substructure　sensitivity　method　is　illustrated　through　an　11-storey　building　under　both　single-and　multidamage　cases.　Both　the　damage　locations　and　the　extent　can　be　effectively　identified.　By　comparing　it　with　the　identical　results　of　global　sensitivity　method,　the　proposed　method　can　be　faster　in　detecting　the　damage　location　and　more　stable　under　multidamage　cases.　Since　this　substructure　sensitivity　method　only　needs　to　update　sensitivity　matrix　in　the　substructure　with　relative　small　number　of　DOFs,　it　may　save　much　computation　effort　and　become　more　efficient.