Abstract: An element-level damage index, damage index of laminated element, was proposed for composite laminate structures that can comprehensively reflect the degradation of load-bearing capacity, which can reflect the damage of stiffness in both internal and external directions and has the advantages of fewer parameters and easier identification. In order to ensure the rationality of the proposed damage index, mathematical and mechanical operators was used to equate the element-level damage index with the material-level damage index, and the differences between different damage indexes in characterizing the degree of damage were compared. The damage identification process of composite structures based on element-level damage parameters was also proposed, i.e., the damage elements were firstly screened by using modal strain energy change ratio, and then the damage degree of the candidate elements was identified by using optimization methods. The proposed method was validated by numerical examples and an experiment work, and the correlation between the elements of the element-level damage parameters was analyzed and the damage identification process of the composite laminate structure based on the element-level damage parameters was validated. The results of this paper complement the existing theory of health monitoring of composite structures.