Abstract: RC structures may damage during their lifetime with the effect of loads, earthquake action, and other factors. And the damage is harmful to the safety of the structure. To guarantee the safety of a structure, it is very important to detect and identify the structural damage at the earliest stage during its lifetime. Based on the characteristic of mult-i resolution of wavelet transforms, a damage identification method, namely delamination wavele-t transform search method, is proposed, which can be used to have an online detection of the occurrence and the location of damage inside RC structure. Numerical simulation for a RC frame verifies that the method is feasible theoretically. Then a model of three-story RC frame is made and tested on a shaking table and the damage of the model structure is identified using the proposed method. It is confirmed that the analytic results of wavelet transform method agree with the results observed in the test.