Abstract: The formation process of the system composed of fault band and elastic rock block and the shear displacement distribution across a fault band were modeled numerically by FLAC. The adopted failure criterion was a composite Mohr-Coulomb criterion with tension cut-off and the post-peak constitutive relation of rock was linear strain-softening. Once two shear bands combine to form a fault band, the system is formed, subsequently leading to the decrease in load-carrying capacity of the system. On one side of the fault band, snap-back occurs due to the sharp recovery of elastic strain in strain-softening process, indicating the unstable failure. Nearly uniform displacement distribution is observed outside the fault band. A higher displacement gradient exists within the band and increases with the decrease in load-carrying capacity of the system. Snap-back of the zone far away from the loading end is the earliest. Then, the size of the snap-back zone propagating towards the loading end increases until snap-back of the entire system takes place. The process only needs a few time steps, reflecting the abrupt occurrence of instability of the system. Snap-back of the entire system occurs in the strain-softening stage of a stress-strain curve.