Abstract: Creep tests were done to study the creep characteristics of two kinds of rockfill materials by use of triaxial-rheometer.It was concluded that the time dependent volumetric strain and generalized shear strain were fit for the law described as hyperbola respectively.Based on the elasto-plastic constitutive model with oblong-parabola double-yield surface,Yin Zong-ze proposed the preliminary framework of a creep model with double-yield surface to consider creep characteristics of rockfill.According to the creep characteristics of rockfill,the model was applied to simulate the shearing creep tests and the method of determination of model parameter was also proposed.As compared with the test results,the propased constitutive model was proved to be reasonable and effective.It was shown that the proposed model could reflect the visco-elasto-plastic behaviors,dilatation and shrinkage of rockfill materials,and it was also applicable to all kinds of loading conditions.