Prefabricated vertical drainage plate (PVD)-vacuum preloading method is one of the effective methods commonly used to improve the dredged slurries. However, in the process of using the vacuum preloading method to improve the dredged slurry, a dense area (soil column) with a gradually decreasing radius from top to bottom will be generated around the PVD, which delaying the soil consolidation rate. Based on the above phenomena, this paper assumed that the soil column radius attenuates linearly with depth, and based on the assumption of equal strain, and the Hansbo's consolidation theory, the consolidation equation considering the change of soil column radius with depth is deduced. At the same time, by calculating the above equation, the influences of the permeability coefficient, the radius of the soil column and the variation of the radius of the soil column along the depth on the soil consolidation rate were explored, and compared with the existing laboratory test data. The result shows that the smaller the permeability coefficient of the soil column, the slower the dissipation of pore water pressure, and the slower the consolidation rate. As the soil column radius gradually increases, the soil consolidation rate gradually decreases. The smaller the residual coefficient after the attenuation of the soil column radius, the greater the attenuation degree of the soil column radius along the depth, the smaller the influence on the soil consolidation in the weak area, and the faster the soil consolidation rate. In the case of considering the soil column radius attenuation with depth, the calculated results in this paper are in good agreement with the experimental results.