Abstract: To well describe the stress-stain behaviour of sands, generally, a state parameter based on the critical state void is used to establish the elastoplastic constitutive relations. However, it is difficult to obtain the critical state parameter in the triaxial drained tests for dense sands. For the phase transformation state, being a characteristic state, its related parameters are easy to be measured. Based on the phase transformation state and considering the stress-induced anisotropy, the state parameter is defined, and a bounding-surface constitutive model for saturated sands is established. Finally, utilizing the provided model parameters, the simulated results fit well with the test ones and realistically reflect the strain hardening and softening characteristics for dense sands.