An effective crack identification method has been developed based on the dynamic behavior of a cracked beam. The nature frequencies of a generally supported beam with crack are calculated by Rayleigh-Ritz method. The crack is then identified from the changes of the nature frequencies caused by the appearance of crack. A hybrid PSO (Particle Swarm Optimization) algorithm is employed as a global search technique to back-calculate the damage. Numerical experiments are carried out on beams with different crack damage. The results demonstrate that the proposed method is able to effectively and reliably locate and quantify the crack in the beam with elastically restraint against translation and rotation.