We propose a hypoplastic model to capture the short-term and long-term creep behavior of granular material by incorporating grain breakage and wetting effect. In the proposed model, the variable critical state line is adopted to assess the effect of grain breakage on the strength and deformation. In addition, a piecewise degradation law for the creep deformation is adopted to evaluate the wetting effect. The proposed model is verified by predicting a series of laboratory tests.