Gudehus-Bauer hypoplastic constitutive model and the determination of its parameters are studied in the paper. Confined compression test is used to determine the parameters hs and n of hypoplastic constitutive model for rockfill materials. According to the derivation of the model

the relationships between the parameters

and the confining pressure are established

and new fitting parameters are proposed. Considering the dilatancy for rockfill materials

a new term of volumetric strain is added into the linear term in the model with a good fit to the axial strain-volumetric stain curve of triaxial consolidated drained tests. The new parameters of the model and the improvement on Gudehus-Bauer hypoplastic constitutive model are verified by means of rockfill large-scale confined compression test and triaxial consolidated drained tests. Compared with the test results of rockfill materials

the present model and its parameters can simulate the stress-strain characteristics of rockfill materials

and can improve the simulated axial strain-volumetric stain curve. Finally

the simulation to the triaxial consolidated drained test in loading-unloading condition by the improved Gudehus-Bauer hypoplastic constitutive model is carried out

and the results show that the improved model has a certain application of unloading.