Research conclusions:The Cambridge model belongs to the isotropic hardened elastic mode,l which is adaptive to the soft soil in the subgrade experiment section ofBeijing-Tianjin Intercity Railway with consideration of the water-press yield characteristics, the press rigidity, the shearing shrinage and the effects of load and download. The determination method for the test parameters of the model is simple for easy usage. Using the modified Cambridge model as the constitutivemodel is scientific and resonable. The testcurve is obtained from the ordianary triaxial compression test for providing the necessary parameters to the Cambridgemodel and providing the basis to numerical simulation calculation. The accuracy ofK0consolidatin test is improved and the model parameters are optimized through upgrading the triaxial device. These parameters can be as the reliable parameters to calculation of post -construction subsidence of the subgrade ofhigh -speed railwaywith Cambridgemodel.