Essential differences in stress state and reinforcement mechanism exist between underwater vacuum preloading and preloading combining vacuum with overlying water on the membrane. Specifically，the total stress does not change during underwater vacuum preloading. In contrast，the total stress in soil increases with the thickness of the overlying water on the membrane in preloading combining vacuum with overlying water on the membrane. The reinforcement mechanism of underwater vacuum preloading is the same as that of onshore vacuum preloading，namely that on the premise of the same total stress，vacuum pumping reduces the pore water pressure and further increases the effective stress. The increasing amplitude between the effective stress before and after underwater vacuum preloading is independent of the water depth，with a theoretical maximum value of 100 kPa. The key construction process of underwater vacuum preloading mainly includes membrane laying and sealing and the selection and layout of the vacuum pump. A combination of sealing with an overlying sealing membrane and vacuum pumping with a jet pump similar to that adopted in the field test in Norway is advisable for the sake of a favorable reinforcement effect. However，factors influencing the construction site of underwater vacuum preloading are complex，demanding the selection of the scheme with the optimal cost performance according to the actual situation on site. Integrating the functions of the sealing device，filter pipes，and membrane outlet device，the patented technology of the sealing membrane laying device for underwater vacuum preloading is available for the sealing membrane laying and sealing in a completely underwater environment，and it reduces underwater operation，It is especially suitable for small-scale seabed soft clay reinforcement for suction bucket foundations in the field of offshore wind power.