The structural damage has a certain effect on structural dynamic characteristics，and it is an effective method to use the change between the modal parameters of damaged structure and undamaged structure.However，it is difficult to obtain the modal parameters of structures which in intact state，and the damage degree is more difficult to determine.To counter the above problem，we putting forward a damage identification method based on the fitting curvature of damaged state，I.e.fitting displacement modal of intact state from displacement modal of damaged state firstly，then getting curvature modal from the fitting displacement modal，judging the damage location based on mutations of real modal curvature relative to the fitting curvature modal；introducing relative change of curvature，the damage location parameters and modal order as the feature vector of damage sample，determining structure damage degree through the support vector machine.The instance analysis shows that the proposed method can detect the damage of pile foundation of the piled wharf.