Abstract: The stress-strain relationship of coarse-grained soils is closely related to soil density. The regular constitutive model cannot consider the effect of initial void ratio on mechanical behaviors of coarse-grained soils. In this paper, a two-yield-surface model is proposed for coarse-grained soils based on triaxial tests. The two-yield-surface model using a state parameter so that can reflect the influence of soil density on the peak stress ratio, dilatancy rule, strain hardening or softening rule in shearing of coarse-grained soils. The stress-strain expressions of this model were also deduced. Several kind of coarse-grained soils test results were used to verify the adaptability of the proposed model, results showed that the model predictions are consistent with test results.