The earth crust consists of tectonic plates, faults and the fault gouges at their boundaries. In the case of studying such an issue as quasi-static mechanics on the seismic precursory spreading, the crustal lithosphere must be treated as a granular system consisting of large-scale discrete grains. In the process of seismogeny, the rock blocks driven by tectonic forces induce a stick-slip motion by overcoming the friction and the boundary resistance. When the fault gouges between blocks are squeezed and their strength increases to a certain degree, the next block will be pushed to generate a stick-slip motion and the successive rock blocks move gradually in the same way. As in any granular system, the distribution and transfer of force and the movement of the rock blocks must be in the chain-like form. This model is not only reasonably deduced from the physical bases, but also supported by many actual observations. In this work the distribution of force-motion-deformation and the spreading time sequence are given with the simulated experiments and analysis. The main feature of the generated precursory information is described. The essential difference between the understanding of seismic precursor led by viewing the crustal lithosphere as granular system and that as continuum medium is presented. How to acquire effective seismic precursory information as well as how to associate it with the occurrence of earthquake is discussed. Some of the seismology problems are explained reasonably, which can be hardly understood from the continuum medium view point.