Numerical solutions of the plastic zone and deformation distribution along tunnel wall due to excavation are presented in this paper. These solutions are obtained from elasto-plastic finite-element analysis, which assumes the Hoek-Brown or Mohr-Coulomb criteria, and the analyzation is performed to simulate a tunnel section far away from the excavation face, where the three-dimensional effect can be neglected. Factors, including the effects of anisotropy in the initial stress state and the tunnel shape on the plastic zone around an excavated tunnel have been examined. Furthermore, a concept called "the characteristic-line family of rock mass" is proposed to describe the varying relations between normalized stress and normalized deformation at various points on the tunnel wall in gradual unloading process due to excavation. The characteristic-line family of rock mass appears to depend on the rock mass property and the tunnel's characteristics.