Abstract: The high vacuum densification method (HVDM) and the deep well dewatering method are proposed to eliminate liquefaction of deep liquefied soil layers intersected with soft clay with high sensitivity in Caofeidian Sewage Treatment Plant. In the improvement process of deep subsoil, groundwater level and surface settlement are monitored, and the liquefaction is evaluated by means of the SPT tests before and after soil improvement. The average settlement during the dewatering preloading and HVDM process is 24 cm and 37.8 cm respectively. The SPT N-value after soil improvement is more than 12 blows, so the liquefaction is totally eliminated from ground surface to 8 m in depth, and most liquefaction is eliminated from 8 m to 15 m in depth. The liquefaction level of structures is assessed to be scarce to slight. The proposed method provides a new way and project experience for similar projects with deep liquefied soils.