The principle and process of the parallel seismic for the integrity of piles of existing structures is introduced. A 3D finite element model for the pile-soil system is established for impulse responses. Under saturated soil or unsaturated soil condition
some vibrating velocity-time histories at different depths in the parallel hole are obtained with the numerical model. It is shown that the length and 1D P-wave velocity of a pile are easy to determine from the features of the mentioned velocity-time histories. Results indicated that the PS method is a new suitable nondestructive test to evaluate the integrity of piles of existing structures.