Abstract <p>The fabric anisotropy variable and density function have great effect on the mechanical property of anisotropic sand. Based on the anisotropic critical state theory (ACST), a modified anisotropic hypoplastic model is developed by incorporating the relation between fabric anisotropy variable and density function into the nonlinear part of the constitutive model. The applicability of the improved anisotropic hypoplastic model is validated by comparing with the existing model and experimental data. As a result, it is found that the modified model can well predict the critical state response of anisotropic sand.</p>