Abstract: Internal erosion causes the loss of fine particle within soil, which not only alters the permeability of the soil but also exerts a significant influence on its mechanical behavior. In this study, the salt dissolution method was adopted to simulate the fine particle loss induced by internal erosion, enabling precise control over the amount of fine particle loss. Subsequently, triaxial shear tests were conducted on the specimens after salt dissolution to quantitatively analyze the effects of fine particle loss and stress state on the stress-strain behavior of the eroded soil. The experimental results show that fine particle loss leads to significant volumetric contraction of the soil, and high confining pressure exacerbates this volumetric contraction trend. The initial secant modulus decreases with the increase in fine particle loss ratio, and high confining pressure further aggravates the modulus softening caused by erosion. The dilatancy exhibits a non-monotonic variation with the increase in fine particle loss ratio and is regulated by confining pressure. The critical state line shifts upward as the amount of fine particle loss increases. Based on the equivalent void ratio, a normalized critical state equation was established. By introducing the fine particle loss ratio and the average effective stress during erosion into the state-dependent elastoplastic constitutive framework, the hardening parameters and dilatancy parameters were modified, and a mechanical constitutive model for eroded soils was constructed. Both the stress-strain curves of soil after salt dissolution-simulated erosion and actual seepage erosion were simulated by the model, demonstrating that the established model can reasonably predict the mechanical response of soil under different erosion degrees.