At present,academic circles do not have a unified understanding of vacuum negative pressure transfer law above and below the underground water level,and of mechanism of effective stress increase above and below the underground water level in the process of vacuum preloading.This paper analyzes the changing of effective stress caused by the total pore water-head change in the whole press of vacuum preloading,and discusses the transfer law of vacuum negative pressure in soft soil from another angle.The research results show that the vacuum pressure can be transferred not only above the underground water level,but also below it.It will decrease with the penetration resistance;both the vacuum pressure and the lowering of groundwater level will cause the increase of soft soil effective stress at any point,and the increasing effective stress expression is uniform for any point both above the underground water level and below it;the degree of vacuum preloading reinforcement is associated with the depth of the underground water level,and the deeper,the worse the reinforcement effect;in the process of reinforcement,the groundwater level will decline,but do not drop.