Abstract: In this paper, the process of continuous loading consolidation under the constant rate loading is analysed by FDM; and the characteristics of the pore pressure distribution in the sample and deformation rate of the sample near the preconsolidation pressure are explained according to Tavenas' plug theory. A great deal of results from computer simulation and experiments show that a typical fluctuation appears on the curve of the sample deformation rate versus the average effective pressure, which is obviously interrelated to the preconsolidation pressure. Mechanism leading to the fluctuation phenomenon is discussed and a method of determining the preconsolidation pressure is advanced,