Abstract: Based on a series of triaxial compression tests, the writers get the Duncan Chang model parameters of the composite sample, the mixed sample, the curve added method, the parameter added method and the layered sample. The results of the tests and computation show that the pile soil interaction should be considered in the study of the composite ground by FEM. It is shown that the parameters of composite sample and numerical tests in FEM are reasonable and they should be replaced by that of layered sample in the area where horizontal stress is greater than vertical stress.