Abstract: Within the framework of generalized plasticity theory, the plastic modulus is modified by adding two correction factors to enhance the adaptability of model under high confining stress, thus the generalized plasticity model for sand is successfully transformed into the model for rockfill materials. The modified P-Z model has fewer parameters, all of which can be easily determined, and it is relatively practical and can be extended into a state-dependent constitutive model. The expression for plastic modulus is simple and can be degenerated to that for isotropic compression tests. The modified model can well simulate the stress-strain behaviours of rockfill materials of triaxial tests and can aslo capture the stress-strain features under other stress paths.