Abstract: This paper describes an analysis on identification of structure damages in high arch dams using the model modification of response surface method with application to a case study of the Ertan dam. This method uses measurements at the gauge points that were carefully located considering sensitivity and accuracy of the response surface, and divides the dam body into sub-regions of different reduction in elastic modulus so that a different damage parameter can be used for the reduction in each sub-region. Then, relationships of the dynamics at the gauge points versus the corresponding damage parameters are represented by certain functions charactering the response surface, and therefore the damage features can be obtained via optimization using a genetic algorithm. This response surface method avoids repeated calls for FEM calculation in damage identification and thus lowers computational cost. To improve noise immunity, a technique of using multiple measurements is suggested in this paper. Numerical results show that our method can effectively identify damages in high arch dams.