Research conclusions :(1) The unload standard of vacuum preloading， should be controlled by the rate of settlement and the degree of consolidation，the rate of settlement is less than 1 to 2 mm/d for 5 to 10 days，and controlled by the degree of consolidation according to the need of post - construction settlement. The load level should be considered for the degree of consolidation，and the total load level should be considered for calculation of degree of consolidation，or the total final settlement as the general settlement under total load，to calculate the degree of consolidation. Especially for high speed railway，the rate of settlement should be less than 1 mm/d for 5 to 10 days. (2) The laws of the rise and dissipation of pore water pressure are basically identical to the settlement rate with load. (3) The settlement will still increase slowly with vacuum unloading， but the settlement rate is lesser. Due to the change of the stress boundary conditions，a certain period should be guaranteed after the vacuum preloading unloads. (4) The transfer law of vacuum with time and depth in different medium is different，and it is suit to transfer for vacuum preloading stress by the plastic drainage plate channels. (5) The research result can be used for design and construction of high - speed railway.