Abstract: The expressions for the mean curves of the attenuation of dynamic shear modulus ratio and the increase of damping ratio of rockfill materials are given by means of the statistical methods. A modified R-O constitutive model with variable parameters, which reflects the nonlinearity and hysteresis of rockfill materials, is established. The model parameters R, mtml_21-1015_bak/img_1.png11.012.0and reference shear strain are discussed. Based on the modified model, a dynamic dissipation incremental function is formulated. Then the corresponding yield surface and energy dissipation characteristics are analyzed based on the generalized thermodynamics, and the mechanism of dynamic stress-strain and the second threshold strain are discussed for rockfill dam materials.