Modal　parameter　identification　of　structures　need　extract　information　from　data　using　signal　process　method.　In　this　paper,　a　newly　developed　signal　processing　technique,　Empirical　Mode　Decomposition　(EMD),　is　implemented　to　decompose　data　set　into　several　intrinsic　mode　functions　(IMF)　by　a　procedure　called　sifting　process.　EMD　can　be　regarded　as　an　adaptive　high　pass　filter　and　needn＇t　set　bandwidth　in　advance.　By　using　intermittency　frequency,　the　sifting　process　can　overcome　the　difficulty　of　mode　mixing　and　decompose　data　to　modal　response　functions.　But　the　decomposition　is　essentially　defined　by　an　algorithm,　and　therefore　of　not　admitting　an　analytical　formulation　which　would　allow　for　a　theoretical　analysis　and　performance　evaluation.　It　still　needs　to　be　better　understood.　A　case　study,　simply　supported　four　storey　frame　structure,　is　presented　to　show　the　applicability　of　the　present　technique.