The behavior of granular materials during loading depends on the level of stresses. When confining pressure increases, the peak shear strength, the residual shear strength and the stiffness gradually decrease; besides, the volumetric behavior is shown to be influenced by the stress level. In this paper, such effects, due to changes in stress levels, have been incorporated into a modified von Wolffersdorff hypoplastic model. For this purpose, reference void ratios and exponent α and β, the parameters of the original hypoplastic model are modified using experimental data. The performance of the proposed model is demonstrated by using simulated triaxial tests on Hostun sand with cell pressures up to 15 MPa. The study shows the ability of the improved model to highlight the behavior characteristics of granular materials in dilatancy and (peak) resistance under high stress better than the original model.