Long-term performance of geogrid is dependent on the viscoelastic behaviors for longtime period. Viscoelastic properties are mainly influenced by not only creep deformation behaviors at the constant confining load and temperature but also stress relaxation behaviors at the constant strain and temperature. In this study, elastic and viscose mechanical model was suggested and applied to examine the viscoelastic properties of geogrid. Experimental results of creep and stress relaxation tests of geogrid were compared to verify the new concept mechanical model.