A new damage-identification method based on vibration transmissibility and PCA（Principal component analysis） is presented.Firstly

the vibration transmissibility between two locations of the healthy structure is served as referential samples

and the vibration transmissibility between the same two locations of the damaged structure are constructed as testing samples.Secondly

the testing samples are added into the referential samples separately

and several original data matrixes are constructed.Then

the PCA is used to extract the first two PCs（principal components） of these matrixes

and the corresponding control ellipses and T2control charts are constructed.The distributing of the first-two order PCs in the control ellipses and T2control charts are used to identify whether the structure is damaged.At last

the steel frame experiment is used to verify the validity of this method

and the index of TAC（vibration transmissibility accumulating change ratio） is introduced to identify the damage location.The results show that the index can identify single damage location exactly.