Considering large errors of damage identification during actual monitoring process, a two-stage detection method based on the improved particle swarm optimization(PSO)algorithm was proposed. The algorithm is then used to detect the structural damage locations preliminarily,and to validate the locating results and determine the damage extents precisely. The comparisons between the simulation and experiments show that the first phase of damage identification reduced the number of suspected damage locations, making the search domain of the second stage based on the improved particle swarm optimization algorithm significantly reduced. The presented two-stage recognition method can identify the damage locations and detect the damage extent precisely for multi-damage and small damage,with considerable capacity in anti-noise.