Abstract: An inverse analysis model for identifying internal defects (inclusions) in the structure using a combined method of the extended flnite element method (XFEM) and the genetic algorithm (GA) is proposed. The discontinuous displacement mode introduced in the displacement function of the XFEM makes it possible to generate a grid independent of the discontinuous interface of the structure. The locations and the size of defects are determined by a modiflcation of the level set function in the study. The GA has a global and local optimization ability in each iteration process. The fltness value of the response determines whether the iteration should continue or not. Two numerical examples including a single circular defect and multiple defects are analyzed, and the locations of the response measuring points in the structure are also discussed. Results indicate that the inversion model presented in the paper can accurately identify the locations and the size of a single defect or multiple defects in the structure.