Abstract: The polyimide films were placed into composites before solidifying in order to simulate the composite laminations damage. The inherent frequency of the composites with and without damage was tested by using the free vibration method. The damage positions of the composite laminations were identified by using the frequency dactylogram. The detection results show that the frequency dactylogram can be constructed using the frequency data of structures，which is only related with the positions of damage and not the degree of structural damage. The orientation of structural damage can be carried through making use of such frequency dactylogram. The method is proved easy and efficient in solving composites damage problems.