Abstract: To supplement the engineering property data of undisturbed soft plastic clay in Kunming, this study systematically measures its physical and mechanical parameters via laboratory tests to reveal the evolution laws of physical properties, consolidation deformation, shear strength, and permeability. A series of laboratory tests were performed on undisturbed soft plastic clay samples collected from the foundation pit excavation of the Northwest New City Digital Economy Industrial Park Project in Wuhua District, Kunming. The basic physical properties, consolidation-deformation characteristics, shear strength, and permeability of the soft-plastic soil were analyzed. The results indicate that the soft plastic clay is characterized by high natural water content, high compressibility, and low shear strength, indicating unfavorable engineering properties. The consolidation coefficient reaches its peak at approximately 100 kPa, presenting an obvious stress-dependent feature. The permeability coefficient is at a medium-low level and decreases with the increase of consolidation stress and the decrease of void ratio. The parameters obtained can provide data support for engineering analysis of similar soils. The nonlinear variation of the consolidation coefficient and the correlation mechanism between permeability coefficient, stress, and void ratio provide a theoretical basis and parametric reference for solving problems such as “large excavation rebound and difficult-to-control support deformation” in soft soil foundation and foundation pit engineering in the Dianchi Lake basin.