Investigating　weak　parts　of　the　structure　is　one　of　the　most　important　issues　for　improving　the　stiffness　of　the　machine　tool.　However,　studies　show　that　overcoming　the　static　deformation　is　a　challenging　problem　in　practical　structures.　In　the　present　study,　the　dynamic　hammer　testing　approach　is　applied　to　analyze　the　cantilever　structure　of　the　machine　tool　with　elastic　support.　Accordingly,　a　new　weakness　index　(WI)　is　proposed　to　identify　weak　parts　of　the　cantilever　structure　with　an　elastic　support.　Then　the　cantilever　beam　with　the　elastic　support　is　numerically　simulated　and　weak　parts　are　modeled　as　stiffness　reduction.　In　this　regard,　finite　element　(FE)　simulations　are　carried　out　to　evaluate　the　effectiveness　of　the　WI　method　in　several　scenarios　with　single　and　multiple　weaknesses,　including　the　noise　case.　In　the　combined　structure　of　the　tailstock　and　the　bed　of　the　machine　tool,　sensors　are　utilized　to　collect　vibration　data.　Furthermore,　the　dynamic　characteristics　are　calculated　through　the　modal　state-space　method　to　obtain　the　stiffness　data　at　zero-frequency.　Then,　weak　parts　of　the　structural　stiffness　are　identified　based　on　the　weakness　index.　It　is　found　that　the　FE　simulations　are　in　an　excellent　agreement　with　the　experiment.　Therefore,　it　is　proved　that　the　WI　can　accurately　identify　the　weak　parts　of　the　machine　tool　cantilever　structure.