For some of granular materials with large cohesive force, such as strong bond soil or cementitious sand and gravel and so on, their macroscopic creep behavior is mainly dependent on the properties of particle contact under low stress conditions. This paper aims at proposing a two-dimensional isotropic creep property of granular materials through the granular micromechanical approach. To achieve this objective, firstly an appropriate rate-dependent force-displacement relationship is introduced to describe the discrete inter-granular properties of granular materials. Secondly, with help of the Laplace transform, the solution for overall behavior of granular materials in the framework of linearly elasticity can be directly used for the solution of the associated linearly viscoelastic problem in the Laplace space; and then, the main problem is to accurately produce the inverse Laplace transform in the time domain. Thirdly, by taking respectively Reuss static, and Voigt and general kinematic localization assumptions, we obtain analytically the corresponding overall creep behavior of granular materials. Further, the upper and lower bounds of overall creep property are established. Finally, the obtained results compared with the numerical simulation by PFC2D are provided to illustrate their validation.