Abstract: The pore water pressure monitoring is one of the important contents of the monitoring hydraulic reclamation silt foundation under the vacuum preloading, and the variation of the pore water pressure can reflect the development of effective stress in the process of foundation reinforcement. Based on the pore water pressure monitoring data, the authors explain the increasing of the pore water pressure in the early stage of the vacuum preloading with the Mandel-Cryer effect, analyze the reasons why the Mandel-Cryer effect happens in the hydraulic reclamation silt under the vacuum preloading, and obtain the duration of the Mandel-Cryer effect that reduces along the depth when the hydraulic reclamation silt is under the conditions of the vacuum preloading. At the same time, considering the soil consolidation state, the transfer of the negative pressure and the engineering environment, the analysis results indicate that the variation of the pore water pressure in the hydraulic reclamation silt foundation under the vacuum preloading is influenced by soil consolidation state, transfer of the negative pressure and water pressure on the sealing membrane.