This paper deals with the classification of piles,the multiple factors responsible for the defects and the necessity of perfection inspection.It is held that the reflected wave theoretical basis and the activation and receiving sensor constitute the crux of the inspection technique for one dimensional rods. The consistency of the frequency interpretation of reflected wave signal with the transient mechanic impedance method is illustrated with practical engineering examples.The paper also expounds the theory and grounds of applying sonic transmission method to inspect the perfection of the foundation pile,the discrimination basis and examples of the inspection,and the latest sound CT technique and its inspection achievements.