The identification of early partial damage in critical parts is of great significance for the safety of the structure. The early detection of the damage can provide basis and support for the use and maintenance of the structure. The dynamic strain of the structure is tested by fiber Bragg grating sensor. At the same time, the dynamic strain response characteristics of the structure are extracted by using the strain modal identification technique. A damage identification index is proposed based on strain response characteristics to identify the damage degree and location. The experimental results show that the dynamic strain response is sensitive to the local damage, and the damage identification index can reflect the degree and location of damage, which can achieve the purpose of structural early damage identification.