Based on the Lianyungang Refining and Chemical Xuwei Cable Tunnel Project, considering the unsaturated hard shell layer that occurs during the vacuum preloading process, indoor model tests were conducted to study the water transport mechanism during the vacuum preloading process, combined with relevant theories of unsaturated soil. The results showed that the groundwater level continuously decreased during the vacuum pumping process, the upper soil became unsaturated, and the pore water pressure showed negative values; The transport of water in the saturated zone is a process of continuously merging and converging towards the drainage plate, while the water in the unsaturated zone converges towards the drainage plate and vaporizes. Under the cycle of water vaporization and increased matric suction, the pore water pressure further decreases, and the soil can continue to consolidate.