Soil deformation has a significant stress path correlation, and the loading along different stress paths will have different stress, strain and strength properties. Understanding the stress-strain relationship under special stress paths such as lateral unloading is of great significance to the in-depth study of soil constitutive models and engineering design of foundation pit excavation. A stress-controlled triaxial apparatus was used to carry out lateral unloading triaxial consolidation drainage shear tests on a remodeled sample of silty clay in a certain engineering in Nanjing under the condition of K₀ consolidation, and the effect of dry density under the lateral unloading path was studied. The influence laws of the stress, strain and strength characteristics of silty clay are established. An empirical formula for the change of the internal friction angle of the soil due to the change of dry density is established, and an empirical formula for the lateral strain of the soil under the condition of lateral unloading is proposed. A method for estimating the ultimate displacement of the retaining structure of a foundation pit based on the proposed formula is proposed.