A　simply-supported　reinforced　concrete　beam　bridge　was　chosen　to　investigate　its　dissipative　characteristics.　The　accumulated　damage　of　the　beam　was　simulated　by　a　static　loading　test,　and　the　change　of　dissipative　characteristics　with　loading　damage　was　tracked　by　a　shock　loading　test.　The　mechanics　of　damping　ratio＇s　change　with　crack　damage　was　analyzed,　and　a　new　index　of　dissipative　characteristic　(adjacent　periods＇　dissipative　ratio)　was　presented.　The　analysis　results　show　that　the　new　index　is　sensitive　to　the　severity　of　crack　damage　and　has　good　noise　immunity.　So　it　can　be　used　as　a　damage　index　for　simply-supported　reinforced　concrete　beams.