Abstract: The soft soil exhibits typical nonlinear rheological characteristics, while the traditional element models cannot accurately describe them. By replacing the conventional damper with a fractal damper and considering the damaging effects of soils, an improved nonlinear fractal derivative Nishihara viscoelastic-plastic rheology model which can fully describe the decay stage, steady stage and accelerated stage of rheology is proposed, and the analytical solution is given. The proposed model is characterized by high precision and simple calculation, and is in good agreement with the test ones, which proves its rationality. Based on the ABAQUS platform, the corresponding UMAT subroutine of the fractal derivative Nishihara viscoelastic-plastic rheology model is compiled, and the validity of the subroutine is verified by the triaxial creep tests and an embankment case. The comparison results show that the established model and developed subroutine can accurately reflect the complete three-stage viscoelastic-plastic rheological characteristics of soft soils.