Abstract: Two post-tensioning tests for bond prestressed concrete beams were used to carry out a static test and a two-stage fatigue test respectively. Under each damage level, the beams were excited by a hammer and their acceleration signals of free vibration were recorded. Then the signals were processed by the blind source separation algorithm and Hilbert transform to obtain frequency-amplitude curves, from which the change of nonlinear dynamic characteristics of the beams with the damage level was analyzed. The strain of the prestressing strand and cracking of the beams under each damage level were utilized to investigate the relation between the change of the nonlinear dynamic characteristics and the damage of the beams. The results prove that the nonlinear dynamic characteristics can be used to detect the damage of prestressed concrete beams.