Abstarct: Damage detection is an important trend in the Structural Health Monitoring (SHM) field that has been the subject of considerable research during the past two decades. Research on diagnostic methods baxsed on dynamical analysis of structures is extended in recent years. These methods can be used as permanent evaluating methods and thus, can prevent further damage to the structure. In this study a novel two stage methods for damage detection of structure is proposed. Static responses and dynamic characteristics of structure will change due to damages dependent on both the damage location and the damage severity. In this study, an approach for damage detection of large-scale structures is developed by modal strain energies (MSE) and Bat Algorithm (BA). Bat algorithm is new mexta heuristic optimization algorithm that using of this algorithm in field of damage detection is proposed for first time in this dissertation. Modal strain energy is damage index that use from changing of modal parameter to determine the location of structural damages. After determining the suspected damage locations in first stage, the severity of damages is obtained baxsed on variations of frequency between the analytical models and the responses measured in damaged models in second stage. The detection of structural damages is formulated as an unconstrained optimization problem that is solved by BA. To demonstrate the ability of this method for detection of multiple structural damages, different types of damage scenarios in space structure are considered. The results show that the proposed method can detect the exact locations and the severity of damages with a high accuracy in large-scale structures. Furthermore, comparison between particle swarm optimization (PSO) algorithm and BA shows that BA have higher convergence rate and accuracy in damage detection field. Finally, baxsed on numerical example, it can conclude that MSE damage index has better ability in detecting suspected damage elements in comparison by residual modal energy index.