At　present　those　should　be　urgent　to　solve　in　the　field　of　engineering　for　truss　structures,　which　are　research　structural　damage,　performance　reducing　and　reasonably　evaluate　structural　safety　conditions.　In　order　to　improve　efficiency　and　reliability　for　damage　diagnosis,　rate　of　change　in　elemental　modal　strain　energy　is　presented　as　dynamic　index　for　damage　locations　of　beam-type　truss　structures.　The　numerical　simulation　example　of　a　beam-type　truss　structure　indicates　that　the　damage　location　and　severity　in　structures,　with　single　damage,　lighter　ones　and　multiple　ones,　can　be　detected　efficiently　by　rate　of　change　in　elemental　modal　strain　energy　with　only　the　first　order　mode.　The　results　indicate　that　the　proposed　method　based　on　modal　strain　energy　can　accurately　identify　the　damage　location　of　truss　structures　with　the　noisy　modal　data.　Furthermore,　damage　degree　can　be　derived　from　the　amplitude　value　rate　of　change　in　modal　strain　energy　for　the　detected　damage　element.　Compared　to　such　indexes　as　modal　strain　energy　change,　modal　curvature　change　and　rate　of　change　in　modal　curvature　etc,　the　effectiveness　and　advantage　are　shown　for　the　dynamic　index　of　rate　of　change　in　elemental　modal　strain　energy.