Based on Snell’s law for simplified pile-soil models, a series of formulae of time-versus-depth relations of the first-arrival of P wave in the parallel seismic test (PST) were derived and a reasonable method for determination of pile defects was proposed in this paper. An axisymmetric finite element model of a single defected pile in saturated soil was used to simulate the PST. The location, length and Pwave velocity of the defect in the pile shaft as well as the pile length were analyzed with the method presented. The results proved the application potential of the method proposed this paper, which is worth of further verification by field tests.