Both vacuum preloading and vacuum well dewatering can be used for the improvement of soft soil foundation.Apparently，both of them drain out pore water through vacuum and make the soft soil consolidate.However，if the understanding of the key differences between the two technologies and mechanisms is not clear，it is difficult to effectively guide the on-site construction.There are significant differences between vacuum preloading and vacuum well dewatering in vacuum pumping equipment，vertical drainage channels and sealing boundaries.The drainage mechanism of the two is also fundamentally different.The mechanism of vacuum preloading is that the soil mass is consolidated horizontally towards prefabricated vertical drains(PVD) under negative pressure difference，and the upward flow of water in the PVD is independent of gravity.The mechanism of the vacuum well dewatering is that the groundwater level decreases due to the pumping of group wells，thus makes the soil unit weight to change from buoyant unit weight to the wet unit weight，resulting in additional loading and consolidation，and the water inside the well pipe is affected by gravity.On the basis of the difference analysis of process and mechanism，the differences between vacuum preloading and vacuum well dewatering in 10 key aspects are further clarified，including reinforcement mechanism，influence depth，vacuum propagation at different depths，soil horizontal deformation，relationship between upwards water flow and gravity，influence of vacuum pumping location，connectivity state with the outside environment，cause of influence area，changes in groundwater level，and formation of unsaturated zone.