Abstract: The stress-strain relationship of the one-dimensional Xiyuan Model was developed into three-dimensional stress state.The visco-elastic plastic constitutive equation was applied in the model and its vertical strain expression was regarded as the fundamental equation to simulate the test data of the long term oedometer test to get the parameters of the rheological model.This method was very convenient and the physical meaning of the parameters obtained was clear.And the method could also be applied to determine the parameters of other rheological model.