In order to investigate the influence of mechanical properties of geogrids on the deformation and long-term stability of reinforced tailings, a rheological model for tailings reinforced by geogrids has been proposed based on the viscoelasto-plastic model with four parameters for mechanical properties of geogrids under long-term low stress loading condition. In this model, the force analysis of reinforced complexus is divided into two stages, i.e., the elastic and plastic states. The time point when plastic deformation (plastic arrival time) occurs is taken as the dividing point of two stages, and then the constitutive relations of the two stages of reinforced complex are put forward. Results show that the viscoelasto-plastic model with four parameters can accurately reflect attenuated creep and stress relaxation characteristics of geogrids. In the first stage, the stress of geogrids decreases with time, leading to the redistribution of micro-stress in tailings. This continues until the tailing yields and moves into the second stage. In this stage, the overall strain of reinforced composite increases as a result of creep of geogrids. The force of reinforced composite soon changes from first stage to second stage and the overall strain is mainly caused by the second stage. The plastic arrival time is significantly influenced by the Kelvin coefficient of geogrids model parameters and the internal friction angle.