The strain magnitude and the stress level in high earth and rockfill dams were studied based on the field settlement data and the corresponding finite element simulation results of two typical dams with heights of about 250 m. The reasonability of the widely used hyperbolic model and its parameter identification method were analyzed. It is found that the shear strain in 250 m-high earth and rockfill dams can achieve a magnitude of 5%, and triaxial experiments can be satisfactorily used in deformation prediction. However, the stress level in dams is generally lower than those segments of experimental data used for parameter determination, which adds considerable uncertainty to stress and deformation analysis. To use the experimental data at low stress level fully, a polynomial method is suggested to fit the stress stain data and a new tangential modulus model is proposed. It is found that the initial loading modulus under an isotropic stress state is overestimated by the hyperbolic model, while the tangential modulus under a shear stress state is underestimated. The newly proposed model can fit the experimental data better and the degree of uncertainty in the calibrated parameters is considerably reduced, which lays a foundation for improving the reliability of stress and deformation analysis for high earth and rockfill dams.