Through a great deal of calculations，the relationship between defect degree and ratio of amplitude was studied，in which the influence of the characteristics of the soil around piles is considered. By means of theoretical analysis，the influence coefficients of a reduced neck defect or a neck-expanded defect to the next one are derived under the condition that the pile has more defects. The theory and method for determining the defect degree of the pile foundation with more defects are discussed，in which the method of regaining the energy of elastic wave and recurrence formulae are developed. In the time domain，the quantitative analysis of pile with more defects is realized with low-strain dynamic test. Finally，model pile test was performed to prove the accuracy of quantitative analysis theory.