Abstract: A viscous elastic rheological model of 3 parts is used to simulate the rheology of roadbed soil. From the observation data obtained during construction, the geological mechanical parameters are obtained by inversive analyiss, adopting viscous elastic FEM and non linear optimal method and the roadbed settlement after construction is calculated. Then a back analysis program of viscous elastic FEM for soil is given. The back analysis was performed for Shanghai Nanjing speedway based on the program and the satisfactory results were obtained.