Abstract: Upon contact with water, unsaturated loess may transform into under-compacted saturated loess while retaining its large pore structure. During the process of water loss or moisture reduction, the soil will undergo sudden and substantial deformation, posing significant risks to the surrounding environment of the project. The fundamental challenge lies in an inadequate understanding of the unique water-sensitive properties of saturated loess. This study proposes the dewater sensitivity of under-compacted saturated loess. Focusing on the saturated loess around Xingqing Lake and Qujiang Nanhu in Xi'an, by statistical analysis of physical properties indicators, and pore structure testing, the basic properties of under-compacted saturated loess were obtained. Field monitoring and combined laboratory–field experiments from six pumping projects were then used to investigate the deformation and strength sensitivity associated with dewatering. The results show that under-compacted saturated loess presents large void ratio and medium to high compressibility. It is generally in a soft plastic or flow plastic state and has a spatial basis and evolutionary trend of continuous compaction. Under-compacted saturated loess has a strong sensitivity to dewatering deformation, which can be observed in its measured surface settlement of 245.8 mm. A single meter drop in water level can cause soil layer deformation of 2.09-10.65mm/m; the maximum settlement rate can reach 4.5mm/d, with average rate of 0.65-1.14mm/d. The larger the void ratio and liquid index, the larger the deformation of water loss per meter of soil and the faster the settlement rate, indicating a stronger sensitivity to dewatering deformation. Under-compacted saturated Qp₃^eol loess presents rapid rate of water loss deformation to be steady and short duration, with a stable state after approximately 30 days; whereas the steady-rate of water loss deformation of under-compacted saturated Qp₂^eol loess is slow, and the continuous deformation time on the surface is long, generally longer than 150 days. During dewatering. Qp₃^eol loess demonstrates rapid and substantial strength gain, indicating high strength sensitivity; by contrast, Qp₂^eol drains poorly, shows slow strength development, and shows relatively low strength sensitivity. This study advances the understanding of water-sensitive behavior in loess and provides a theoretical basis for risk assessment and mitigation strategies in groundwater-control engineering within similar geological settings.